Before you associate the following UI design with me or Cocoia, let me assure you that I have had no involvement in Picasa whatsoever. With that out of the way, the recently released Picasa Mac version is quite… unique when it comes to UI.
This image illustrates nicely how Picasa seems to use mixed sans and serif typography, wholly custom controls and strange, nonstandard color palettes throughout the app. I must admit I’d expected more from Google; I’ll stick with iPhoto for now.
Update: Michael J. Tsai reports that Google is using a cross-platform toolkit, which also prohibits Picasa from running on PowerPC Macs. Weak.