My own testing of Safari 3.1 on Windows has stalled while I work out and fix an issue with one CPU on the dual processor machine. Right now, that box couldn't work it's way through a session of Minesweeper, much less run Windows in a VM.
Here is a very positive review of the new Safari at Ars Technica. It is definitely worth your time.
We can only benefit from another competitor in this space. IE is not exactly what I think of as a great browser. Firefox has memory issues. Opera is, ah, quirky. In this new version, Safari carries adherence to standards to a new height. It even complies with standards just coming into force now! Why, even Opera doesn't support the full list of what Safari does.
I'm not recommending people install Safari on Windows, yet. Not that my thoughts are going to stop those of you who are computer savvy and know how to manage risk with new software. But I take that stance to John and Jane Doe precisely because Safari's security has not been evaluated in the real world. Should it go a few months without any glaring issues, I'm all for installing it. Just not now. Not yet.