Java mostly lives on the server - it's been a roaring success there, but it's failed on the client for the same reason that our product, VisualWorks didn't get that much traction on the desktop - end users really, really want apps to look and feel the same. We are addressing this by moving towards Pollock
The irony in this is that with Longhorn, the GUI is becoming more variable in appearance and layout, as well as lighter weight. The Longhorn GUI is going to be *more* like the emulated (i.e. "drawn") widgets of Visual Works, but with a more sophisticated drawing model.
By and large people have been successful with the variety offered by DHTML user interfaces and game interfaces. One of the most appealing user interfaces that I am aware of (Hypercard) is also notorious for breaking the user interface guidelines established by the same vendor.
Still, Pollock is a good thing for Smalltalk, hopefully providing the flexibility to access all of Avalon when or if Longhorn finally arrives.