Am I the only one who can't stand transparent windows of any sort? It really distracts me from the contents of the window, and the blur makes my eyes try to focus it, and then my brain tries to process the image.

I'm still waiting for my dream UI: no transparency, but everything other than the current window is slightly out of focus (even the dock or windows bar). When you move the mouse to a new window, it comes into focus. You could even do several levels of focus (if not in a full-screen app): less for visible windows more for background such as dock/windows bar and desktop. I haven't tested this in real life (mockup), so maybe it's been tried and rejected already.