Quite a while ago, I heard about Object databases. Cool concept and all. Now, with the event of ORMs everywhere, does anyone still use any of the Object oriented Databases systems? Are they relevant? Are they practical?
OO databases never got out of a niche market. They are good for some applications - where the data structure lends itself to being represented by an object graph - but never held the compelling advantage over a RDBMS to cross the chasm. The key advantage touted for OODBMS products is the tight integration to the host language - there is no object/relational impedance mismatch.
However, there are still several OODBMS vendors such as Gemstone, Versant or Cardinal who are doing quite nicely with their products. The technology is useful for some types of data structures and can be more efficient than a RDBMS but tends to be weak for ad-hoc queries compared to modern SQL dialects.
As various others have noted, Gemstone is getting a bit of attention due to their support for Seaside and Maglev (a port of Ruby to the Gemstone VM with Rails running on it). We may find this gets the nice folks from Gemstone a bit of press and with it a bit more attention to the OODBMS paradigm.