I was using IE6, then switched to IE7 and finally I have installed IE8.
I used to get a lot of security problems with IE6, but that was corrected y the SP2 for WinXP. Never had a security problem anymore since that. IE6 still had some functionnality flaws from time to time, however.
IE7 was great, providing anything I needed.
IE8 is just like IE7, but with even more functionnalities. So far I am very satisfied with it. I had only one problem though: displaying the Flightsimworld.com forums will cause a freeze of the window. I have to kill IE8 and restart it because it will not respond anymore. Certainly a script problem or something like that...