Really? I have the exact opposite reaction. Every development in OS X has made itself more subtle. Gradients are lighter, windows are softer... The unified 10.5 theme got rid of what I felt was a kitschy plastic feel in the system, and it created a much more intuitive menu set-up where buttons are a part of the top bar. 10.6 takes steps even further — I love the new Dock menus and hope that's the standard from which Apple develops its new look. Some things moved backwards — the new iTunes got more gradient-y and that's an issue — but in general Apple's design is growing more and more subtle.

The default backgrounds are a little silly, yes, but I think when we look back we'll view it like we view 60s typography — perhaps a bit gaudier than we needed, but it was done in a sense of fun rather than a sense of self-importance. The space-age design feels to me like a wink.

I don't know, I don't really feel like an OS needs to look timeless. It seems strange to me to judge an OS's appearance based on how it will look in 10 years, when hardly anyone will care anyway.

Agreed, but it's mostly in that awful background---I ditched that first thing, and everything else is pretty well in continuity with the previous versions.