Hmm. Weird. I just switched to Firefox (I'm at home) and there's little if any difference. I've also got a lot of network traffic going on right now (about 40 KB/s up and 35 KB/s down). Could it be a memory leak issue? Or a processor intensive task? Try building a dedicated user account, rebooting into that account only, and try again. If that solves your problem then you need to use Activity Monitor to see if you have a problem application that is hogging processor cycles or memory.
Oh, and empty your cache in Safari, or better yet empty all your caches using OnyX and run all your maintenance utilities. And repair permissions.
I'm curios now what's going on.