I’ve been taught that you wash your whites with hot water, but this wears out the fabric and elastic much faster, it seems. Educate me - does it make a whole lot of difference, cleanliness-wise, whether I wash clothes in cold or hot water? I’m talking about just your own everyday sort of laundry, not in terms of trying to remove stains like grease or blood or other heavy-duty dirt.
Well, for blood and other protein stains you never want to wash in hot, and you want to be sure it’s all gone before you put it in the dryer. Hot water will set the stain and you’ll never get it out.
That’s not the only issue.
The nature of some fabrics dictates either lukewarm or cold water, in order not to alter the size/dimensions, or to affect some other basic characteristic of the substance. Frex, wool (a protein) shrinks in hot water. In hot enough water, ya can’t ever stretch it back out (hint: google for boiled wool). Some other natural fibers also shrink (cotton, silk), but less. Some artificial fibers - particularly rayon (IIRC, the very oldest artificial fiber) are also very vulnerable to higher temperatures. I’d suggest googling on the particular fiber in order to learn what you shouldn’t do.
<sigh> I just couldn’t do it. Look here
Here’s more:
Among other things, the Cotton Inc. site explains the differences between animal & vegetable fibers
More information than you ever wanted, no doubt. 
also the soap manufacturers often add enzymes to digest protein and blood stains, the enzymes dont work at high temperatures
Anecdotal data point:
I used to take my laundry into the laundromat and pay them $0.60 per pound to wash, dry and fold for me. It beat sitting there for hours, wrestling other folks for the one working, free dryer and so forth.
The guy who ran the place informed me that he only washed everything in cold. You don’t have to pay to heat the water and most laundry soaps are now formulated to work in any temperature water. Your fabrics hold up better and get just as clean. He claimed that anyone who washes in hot is just wasting their money.
FTR, I only wash in hot if it’s something the dog peed on and I’m trying to sanitize and not just wash. I add white vinegar and rinse in cold. Seems to do the trick.
What whites? Due to the difficulty in getting “whites whiter” I have virtually eliminated them from my wardrobe.
According to our youngest son, it makes no difference at all. It also doesn’t matter if you mix colors with whites (just add lots of bleach). Then put everything in the dryer. Anything that does not pass this test must not be worth keeping. 
I wash everything in cold. Cheaper and no chance of shrinkage. This time of year I add a little warm cause the water coming into the house is really really cold an I don’t want to get my hands that cold, thanks.
For the record, I don’t care one bit about separating colors unless the clothes are new and likely to bleed. Then, they get washed with darks (especially underwear, who cares if you get a streak of blue on your black underwear?) and/or towels.
I also never use bleach. Waste of time and money.
This has worked for me for nearly a decade, for what it’s worth.
I’m with Film Geek. Life’s too short to sort by color, fabric, dirtyness, stains, etc. etc.
The only advice I’d give is to use liquid detergent. Powder doesn’t dissolve well in cold water.
I also use cold and I never see any difference in the resulting cleanliness.
My laundry hint: I keep a little squeeze bottle of spot cleaner (I use Simple Green) next to my laundry hamper, so that a spot gets treated right away. If I don’t do this, I’ll never remember what’s spotted at the time of washing later on, and I don’t want to waste time hunting for spots.