I use IE (mainly), Opera and Chrome, I can never get used to Firefox visual elements (icons, fonts, smoothing feels rather unappealing - in contrast to the other 3) so I only use it on occasion.
I had to install IE8 on the bosses PC last week. and it was awful how bluntly Microsoft have tried to wean me away from our preffered Default providers. Listen MS, screw Bing! I will use that and Yahoo! when and if I want. I don't want the MS defaults and I don't want to dig deep so don't make it so hard, Google is good enough ( actually great when I consider the alternatives).
Who uses Yahoo! much around these parts anyway? The ad bloat from mid 90's put me off completely, and I visit on occasion like once or twice every two months.
So on my PC I am sticking to using Googles services and IE7 and Opera and Chrome.