Never! I have grown so far away from IE in the last couple years I can't see myself going back. I also enjoy my FF addons too much to go back (adBlock,Firebug, noscript). When IE is killed (thought I read that IE8 is the end)
and the next MS thing comes out I'll switch. The only time I open up IE is when I am working with an enterprisey app.
I have both FF and IE8 installed. I use both but tend to lean toward IE 90% of the time. But harumscarum you just keep on using FF and wearing your tin foil hat. =)