I've been playing with Opera(on Windows at work and Linux at home) for a month or so now. I'm actually quite impressed. It has all the lovely bits of FF(Tabbed browsing, mouse gestures etc) and seems to be wired a bit more like my brain(which is a very strange and dark place).
For all those thinking of changing to FF there are some nice tutorilas showing you how to get the most out of it. Have a quick Google(thats the box in teh top right
Oh and you can switch it to search eBay etc if you click on the logo of the search engine )