Tom: KDE can be configured to put the menu bar at the top of the screen, Mac-style. Personally, I find that the Mac style just ensures that the menu is always maximally far away from my mouse pointer, which means more annoying mousing, but that's a matter of personal taste.

I've tried KDE on OS X, but AFAICT it's not ready for prime time. I've never managed to boot a complete KDE session (kwin window manager) successfully, although I use Konsole as my main terminal, since Terminal.app doesn't support tabs, iTerm is painfully slow, and glTerm isn't free. I'd really like to see a successful native port of KDE to OS X, but I don't know if anybody's really working on it.

Photoshop isn't an issue for me -- I'm a programmer.