I’m with many others, including Yuval, in saying that Apple porting Safari to Windows is unfortunate. Web developers have basically got 3 main browsers to deal with right now, and adding a 4th isn’t going to help. IE6 is dying, but still prevalent. IE7 isn’t great, but is obviously a force to be reckoned with. Firefox is bloated and slow, but comfy and relatively painless to develop against. Safari is outdated, buggy and less standards-compatible than IE7 or Firefox, often intentionally so (try styling a submit button).
The big claim Apple makes is page rendering performance. Firstly, I hope nobody takes Apple’s performance numbers seriously, they’ve been flat out lying about them across the board for a decade or more. Even if the stats are legit, picking a browser based on page rendering speed is silly, it’s like buying a car that goes 200mph instead of 150mph, when you live in Los Angeles and spend most of the day in slow traffic anyways.
I think Apple ported Safari to force people to support it, since it’s often sidelined due to low usage and its quirky behaviors. I’m really loathe to support a browser that offers no new features yet has a unique set of drawbacks. The solution here is for Apple to abandon the KHTML core and put it’s overstated development resources into the Gecko engine, giving them the ability to Mac-ify and brand a browser, but not impose increased costs on web developers. They should look to their own successful Airport line for how you can drive adoption, leverage/strengthen a standard, and maintain a strong brand at the same time.