I still use Safari on my Macs out of habit.
I use IE6(still haven't gone to 7) rarely, since there are sites/apps I use that use ActiveX.
Mostly I use FF on Win and Linux, although it is getting a little too bulky, 100MB memory usage a lot of times.
I realy like Opera, but I already have two browsers that I use on most machines. If FF keeps getting more bloated then Opera will win out.