I just "released" my first web application using XStreamDB today. The part that has to talk to XStreamDB took less than an hour to write, and was really quite simple to do.
The app is an interface to a database of 641 (and counting) teaching resources, to be used by faculty, grad students, students, etc. to find solutions to problems facing them in the practice of teaching and learning.
The app works really really well right now, and it's completely unoptimized. Page queries returning hundreds of results are spit out in under half a second.
And it's not optimized yet.
XQuery rocks for these kinds of solutions. It's trivial to generate some really funky queries that would be downright scary in a RDBMS-XML solution like the JUD. This app isn't using any of those (yet), but it will...
Here's a link to the application - it's just an early "alpha" build, with no real testing of the code yet, so it may be fragile (or it may be pretty solid - no guarantees yet).