Actually one of the most interesting things at RailsConf was MagLev, which applies the GemStone object persistence engine to Ruby. Apparently there are some pretty big Smalltalk apps out there using GemStone. http://chadfowler.com/2008/6/5/maglev and http://ruby.gemstone.com/
One of the interesting technologies that Gemstone has had in its portfolio for years is the ability to make its data available in relational/SQL DB form. You can have your app running on top of an OODB, but still interface with your Fortune 500 comrades who want to do SQL queries for Crystal Reports.
I had the opportunity to work with Smalltalk/Gemstone in 1994. At that time we thought OODBMS was the next big thing. Programming was easier. However, soon it was clear to me that OODBMS was not the way to go. For example versioning is quite simple in an RDBMS compared to an OODBMS.
