I'm curious why a lot of people / companies seem to be picking up Cassandra lately. I'm not one to peg one "NoSQL" software system against another, but I've be

I'm curious why a lot of people / companies seem to be picking up Cassandra lately. I'm not one to peg one "NoSQL" software system against another, but I've been using HBase for a few months (albeit on a rather limited cluster) and feel that it fits great especially with its compatibility with Hadoop. We use Hadoop + Map/Reduce extensively at Grooveshark. Does anyone have experience in using both systems and can offer a candid account of both?