turns out yahoo has been building their own datastore thats sortof halfway between memcached and cassandra
this post is over a year old but I had never heard of it before
http://developer.yahoo.net/blog/archives/2009/06/sherpa.html
looks like they’ve been busy in the meantime:
http://developer.yahoo.net/blog/archives/2010/06/sherpa_update.html
no talk of plans to opensource it or even make it available as a service though
