I think that it’s pretty safe to assume that by this point you’ve either used Safari on a Mac or you haven’t. I’ve used Safari for a number of years, but it has never become my browser of choice. Why? Quite simply: Firefox is more extensible and Camino is quicker on a Mac.
The introduction of Safari 3 to XP and Vista definitely changes the playing field. It’s tough to say whether Safari will enjoy the same sort of growth that Firefox has experienced over the past couple of years, but being available on both Mac and PC now certainly can’t hurt.
Safari 3 Beta on Windows is going to make browser testing that much easier. Seeing as the iPhone will use Safari as it’s browser du jour, Windows designers/developers will be able to develop and test applications for it without having to own a Mac. I own two older Macs, and will test sites in Safari from time to time, but it’s never been a high priority for me. (Heck, even my site has some issues with the footer in Safari… which I hope to address soon.)
Because it’s not heavily integrated into Windows, you breathe a little bit easier knowing that the browser (probably) isn’t going to suffer from the same problems/exploits that Internet Explorer has to deal with.
Safari’s also going to change the way you view things on the web. Seriously. Have you seen how gorgeous typography looks in Safari? Microsoft ClearType can’t touch it. Neither can any other browser on Windows. I can only hope that Microsoft and Mozilla see Safari on Windows and work to improve how type looks in the browser. Aliased type is easier to read, and gives sites more of a printed-word feel, in my opinion.
Oh, and did I mention that Safari is yet another Apple gateway drug? Between Quicktime, iTunes and now Safari, Apple is attempting to bring part of the Mac experience to PC users. The best thing Apple ever did was open the iPod up to Windows. It makes sense for Apple to release (free) software for the PC as long as it serves as a mechanism to get PC users to buy Mac hardware.
All in all, the introduction of Safari can only be a good thing for users. It probably won’t become the browser of choice for a number of them, but having a choice is what’s most important.