Thanks for starting this thread! Would you believe in all my years of Mac-ing, I never used any of the Themes? Well, this weekend, I downloaded a bunch! And I started using Power Windows, SmoothType, and Greg's Browser!
Whoa, what a weekend. Anyway, now I get to use my beloved Classic OS with all the eye candy of OS X. Currently my favorite theme is Moby, but I'll be playing around with them (all of them!).