I’ve recently started using the In Private browsing feature of IE8 more and more, and no not for Porn!
For testing sites I’m developing or doing a clean Google search, it would usually involved closing the browser, clearing cookies / cache etc. and then restarting. It is now reduced to Tools -> InPrivate Browsing, and bang you’ve got a clean browser session. And I know Firefox supports this, but they really make it unusable if you run Firefox with lots of open tab (currently I’ve 36 and it isn’t a busy day) because it shuts the browser down, opens the private browsing mode and then restores things after it is finished.
I guess I’ve long since used two browsers. Firefox for personal stuff and general web development tasks. IE for Intranet net applications and not the InPrivate feature.
If only someone would invent some proper work spaces for a browser. And some better way of storing/organising favourites.