For a project I am working on now at Onespot we are just beginning to move off RDBMS and onto Cassandra for a subset of our data store. We evaluated against several other solutions including Tokyo, Voldemort and Riak and Cassandra seemed the clear winner for our requirements. We have also done stress testing and been happy with the results.
Wishlist: - rebalancing - Hadoop integration - node replacement that doesn't depend on having the same ip/hostname - multi-insert (so can insert against multiple keys in one request) cheers, Scott
