i vaguely remember someone else mentioning that in a blog I read, but the font is rendered differently, and I don't think it's because safari is alpha or beta or whatever.
The blog article on it was an interesting read. I read another article discussing the different philosophies that Apple and Microsoft have taken when it comes to font smoothing.
The advantage of Microsoft's method is that it works better for on-screen reading.
The nice thing about the Apple algorithm is that you can lay out a page of text for print, and on screen, you get a nice approximation of the finished product.
I think it looks insanely ugly and illegible. I tried using Safari again now that 3.0.1 is out, but quickly quit. I just can't stand it, even aside from the fonts and how poorly it renders pages. The interface is horribly broken compared to Firefox or even Internet Explorer.