IE 6 was a disaster for Microsoft being full of security holes! That prompted many to go with FireFox as a rule. Apple's Safari 3.1 as well as Opera, Netscape, and others became popular due to the IE 6 flop. Safari is literally the fastest browser there to note seeing pages load like lightning.
IE 7 saw the security holes plugged up as well as introducing an antiphising filter in the newer version of IE. Presently I've been waiting for the full not beta version of IE 8 to compare that to 7 and other browsers like FireFox 3.0 and Safari 3.1 used here.