Sometimes it takes a long time to load web pages because the server that contains the web page is really busy (this is often the case for the SDMB). Nothing you can do about this, short of buying the chicago reader a spiffy new server (which I’m sure they would appreciate, but it will set you back quite a bit in the cash department).
Sometimes your ISP is overloaded and creates a bottle neck. Nothing you can do here either, except complain a lot, or switch ISPs.
Sometimes your computer is the target of a hacker, and even if he/she isn’t getting into your computer they are keeping it so busy dealing with the network traffic that it takes a heck of a long time for it to do anything else. This one is hard to deal with, but hackers will either hack into your system, or try for a while and give up. They generally won’t keep up an attack for days on end unless you specifically do something to piss one of them off.
Sometimes the hacker did get in, and your computer is spending an awful lot of time running evil programs in the background, making anything in the foreground slow. If you don’t have a good anti-virus and trojan detector, now would be a really good time to get one. AVG seems to be good if you’re on a budget (it’s free).
Sometimes its adware/spyware choking up your system. Adaware and spybot are your typical cures for these folks.
Sometimes its a normal program on your system that has a bug in it that eats up a lot of memory for no good reason (in programming we call this a memory leak). This can cause your computer to slowly grind to a halt. Rebooting will cure the problem, but running the offending program will cause it to eventually come back. If you find such an offender, see if the company that made it has a patch available.