Continuing to play with doing demos of engineering applications using Ruby on Rails, and in particular the Hobo and ActiveScaffold frameworks that sit on top of Rails. Hobo is nice as long as you have a fairly simple set of concepts to handle. ActiveScaffold is more flexible, but is also a bit more work (e.g. Hobo builds in users/password where you have to add it to ActiveScaffold yourself).
Used ActiveScaffold on one "real" project at for work, which was just a prototype though, with around 30 concepts in the model and it worked out OK. Still some limitations though. It was the front end for a rules engine (jRules from iLog which was recently bought by IBM) so was an interesting architeture. We had to update the data tables from both the Rails GUI and from Hiberbate from the Java accessing jRules. Oracle Express was the database, which poses some problems of its own (e.g. date support is problematic).