Why wouldn't you use Scalaris?
Scalaris is written in Erlang dont know where you got the idea that its Java based http://code.google.com/p/scalaris/
and they've tackled the hard problems first, the update protocols, scaling, etc... adding disk persistence is pretty straightforward, and will be added very shortly Im planning on using it a lot
I'm not going to use it without a disk persistence / snapshot system. My impression is, that in memory databases are not very reliable. If a cluster has only 2 nodes which can go down for maintenance the data is lost. The same, if there is a blackout in the rz and the USVs can only supply enough power for a few hours.
Oracle/DB2 Databases have a lots of disaster recovery features! Business critical data on scalaris without a disaster recovery strategy? Never. So scalaris looses its impact on real business. Maybe it's the best distributed DB i've ever seen, but without those features I'm not going to use it.
There is a Java Connector! But it's written in Erlang. It may be nice to have an scalaris written in Java or JRuby (which can fit in in the Java ecosystem, which has such a big impact on business).
i see scalaris more as a replacement for memcached rather than something like voldemort or cassandra