There is now a kind of global acknowledgement that RDBMS are not well-suited for all new business applications in SOA. I've already mentioned new databases like SimpleDB or Vertica the new project from Michael Stonebraker.
Here is a collection on links about DDD (distributed document databases):
StrokeDB (for Ruby)
http://strokedb.com/euruko2008.pdf (nice and innovating kind of presentation)
CouchDB (written in Erlang)
RDDB (sub-project of CouchDB)