I offer no counter or dissent to your post. However, apparently, the binaries have not yet been posted. Perhaps once they get that crucial detail finished, things will be clear. It appears they haven't even reached an actual beta stage. It might have been better for them to wait until everything was ready to go before launching the site publicly.

Considering the 'front-end' of membase is memcached code, you should be able to use any library that interfaces with memcached to interface with membase.

Out of curiosity, what drew you towards Cassandra over, say, Riak or MongoDB?