I've noticed IE slows down dramatically as time passes after a reboot. I've timed the MSN home page load, and right after reboot it takes 4.5 sec. to fully load. After a few hours it can take as long as 50 sec for the same page to fully load (progress bar disappears). A reboot restores it back to 4.5 sec.
When it is slow, there is very little CPU activity, very little hard drive activity, and very little traffic on my DSL modem. It is like IE is just sitting there, with occasional blips on my modem Tx/Rx LED. I've tried deleting the IE cache, history, cookies, etc, but it doesn't help.
I would reinstall Windows, but I'd like to avoid that hassle if I can.