Simple enough…
What do YOU think the world will be like in 100 years?
Cell phones will look like miracle ear 2000.
Toilet paper will become three little sea shells 
The homogenization of the world. There will be lots and lots of diversity, but it will be distributed more-or-less equally around the world. You can get good Thai food in Mexico City and in Bangkok. Islamic radicals? You can find them in a Starbucks in London or in Panama City.
We have our real lives, and our on-line lives. We may be (probably will be) friendless in RL, but have lots of friends who are also into underaged goats just like us, all online.
This will lead to a weird sort of tolerance. In real life we may get along with a certain group, but online will will avoid them. We will know mostly people just like ourselves. Darn shame.
I’m not sure I get that. My RL friends have always tended to be much, much closer to my demographic than my online ones. I don’t know why that would change in the future.
See 1984 or Brave New World for details.
If we are still here.
Underwater tours of the flooded cities just off the coastlines will be popular. Cellular communication modules will be implanted at birth and will provide music and entertainment 24x7 so that nobody ever has to bother actually thinking for themselves again.
Nothing much will change. Personal motor transportation may die out, replaced by mass transit. Global quality of life might increase a bit, but some will still be rich, some poor. Western countries might be a bit more diverse, but much of the world will look more or less the same. We might have a commercial moon base; orbital space tourism will probably be well developed.
According to my calculations, in 100 years, my Great-Great-Grandkids will be less than .5 miles from the shore. We are currently 10 miles in land. Good thing my property is on a slight hill. 
New York City, London and many others will be protected by huge dike systems. New Orleans will alas be gone, but rebuilt on higher ground. People will complain it is nothing like it was before the bowl washed out for good. Some will point out New Orleans was never the same after Katrina according to historical text and fiction of the time, so get over it, the New ‘New Orleans’ is still wonderful.
If our civilization is still going, I predict we will be running Nuclear Fusion Power, Full Spectrum Solar Power that realizes 50% to 60% efficiency. There will be plenty of wind power and fuel cells. The ICE engine will finally be gone. We will have some form of transport based on an electric motor. Probably fueled by batteries or hydrogen. We might still have Bio-Diesel for trucks and ships. Aircraft will be our last major source of hydrocarbons.
We still will not have personal flying craft or jet packs. Gun laws will be more restricted. Free Speech will be more restricted. There will be a lot of pressure from non western nations where population levels will have completely outstrip available resources. The most developed nations that have low population growth will have clamped down immigration to a trickle. They will use the huge energy boons to continue growing and exporting food, but it will not be enough. Most Petro-Chemicals will be devoted to agriculture by then.
We will have a small moon base and several orbital stations. Low Gravity research will be making huge advances in the chemical science. People will be debating whether it is a waste of time to have a manned mission to Venus and setting up a Mars Colony. Many will argue we need to go as humans need frontiers, many others will argue the expense is too high and we to devote the funds to fighting poverty and starvation.
I could go on, but I need to go, maybe I will add more later.
The Straight Dope will still time out all too frequently.
Jim
We’ll be talking about beach-front properties in Nevada, because California will have cracked off and fallen into the Pacific Ocean.
Not sure what it would be like, but there had damn well better be flying cars for my great-great-grandkids to tool around in.
I’ve never been too excited about flying cars, if only for what happens when the engine fails.
If an ordinary road car stalls, you steer off to the side of the road and coast to a stop. If a sky car stalls, you plummet to your death.
Large portions of the population will be addicted to online environments. In most cases these will be pornographic in nature, but in some cases they’ll be entertainment-based, such as MMORPG’s. As these environments will be 3-D and indistinguishable from physical reality and there will be systems to provide the body’s physical needs while interacting with these environments, the addicts will have no motivation to leave them. Some will be addicted for life. Many treatments for the addicts will be proposed, none totally successful.
Increasing numbers of psychiatric drugs will be available, and the drug corporations will push them aggressively, especially those for children. Schools will require that all students take certain drugs before being enrolled.
The suburbs of Los Angeles will meet the suburbs of Atlanta somewhere in the great plains.
Let’s see, 100 years from now - the cats and rabbits will have taken over the world, because all the humans will be dead from plagues and never-ending small wars.
That’s two very different visions there- one of brutal soul-crushing tyranny and another of happy soul-anesthetizing tyranny.
I’m hoping for the second one. Pass the soma tablets, please.
I see three likely possibilities. A collapse of civilization is the first, from war or the ecology, say.
The second is a society where the economy is mostly automated, and where most people spend their time in permanent or nearly so virtual environments. Most people won’t have jobs, or only token ones; most things will be done by the machines. The economy changes drastically, as many things lose all value, since the machines don’t care about being paid. If they self-replicate, even the initial capital to build them is unneeded. Land, enerergy and raw materials will still be of value, as will personal service, unique objects and to a degree information.
The third is a variation of the second. When total or near total automation becomes possible, the elite has the majority ( 95% + ) of humanity killed as worthless, using bioweapons or robots or something else that doesn’t require human soldiers ( who would balk, as they would no doubt be included ). Society then becomes a small elite supported by machines, probably with a fair sized population of human slaves.
The choice depends on whether we get Republicans or Democrats.
Screwed, it won’t have me in it…
I’m sure there’s going to be some big economic changes, but I also think a lot of it will be stuff that nobody who’s currently alive and sober will be able to predict. There have been changes in immigrant attitudes to Spain in the last 10 years that nobody would have predicted 10 years ago; this is changing things “back home” as well. As people start getting better information about Other Places and Other Peoples, they may be able to make better choices for their own lives… or not. We may be in time to start using fossil fuels in better ways than just burning them before it’s too late… or not. We’ll see coastal towns drowned… or not. Birthrates going down in most countries, there’s no “or not” there; the exceptions to this may be, sadly, those places that are most ravaged by AIDS.
There will always be people who don’t get on the 'net, same as there’s people who don’t read. Whether they’ll end up being the lords or the slaves… hm… how long till next NaNoWriMo?
Wow, lots of optimism in this thread. As a counterpoint to all this doom and gloom, I think the world will get better in ways we can’t even imagine right now. I think energy from the sun will be harnessed much more efficiently and used much more broadly. The Internet will become incorporated into our lives in ways that make it easier. Transportation will continue to improve and change for the better. I hope that religion becomes much less prevalent and people become more rational. Third world countries will have greatly improved living conditions and life expectancies around the world will be much longer than they are now due to improved health and medical technology. They will finally invent a diet pill that works without killing you.
I really do think that humans are basically good and want to do the right thing, and that we try to improve the world around us and often succeed. Cheer up, people.
Oh, thanks for reminding me, Renee - the ones that aren’t killed by the contagious diseases will be stoned to death by the religious zealots.