I'm on XP both at home and at work. I've used Vista once, when we were visiting the hubby's cousin, and wasn't awfully impressed, although I didn't have any problems with it at what I was doing (checking my e-mail and a couple of other sites).
My favourite browser is Firefox, hands down, and the newest version (3.5.2) works quite nicely on my home desktop, unless I have too many programs going on at the same time; then, there will be memory issues, although I've done some tweaking to make the browser take up less memory. At work, I'm on Firefox 2.0.0.2 for almost all of the browsing outside the house; our systems only support IE, but one nice PC advisor installed Firefox for me a few years ago. The only problem with it is that, because we're on XP Professional and I don't have admin rights, I can't update it myself, and the nice PC advisor works a little too far now.
Opera comes a close second, and it was actually my favourite at one time, but unfortunately, too many websites don't support it. At home, I also have IE8, Chrome, and Safari, all of which I hardly ever use.
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People, you and me, are not trusted. The right doesn't like us because we don't do what we're told by our betters, and the left doesn't like us because it secretly thinks we would be on the right given half a chance and a lottery win. And both think we should not make our own decisions, because we might make the wrong ones. ~
Terry Pratchett