I read with interest the SIGMOD paper on Facebook's Cassandra. It looked very interesting, an open source combination of BigTable and Dynamo (PDF) . It appears to be running in production in Facebook serving the very demanding inbox notification system.
So I wanted to try it out. I went to the Google Code project, and it just seemed, well, dead. The instructions for checking out the source are wrong both on the Sources tab as well as in the Wiki. The mailing list has almost no activity. It looks like they are trying to get into Apache incubator, but meanwhile people are asking what's going on, what the status is, and there appears to be no response.
A consideration for using any technology is understanding the strength of the community behind it. You don't want to bet your infrastructure on something where there is no support and you are basically on your own to maintain it.
So, if you know what's going on with Cassandra, please let me know. Meanwhile, I'm going to put it on the back burner and take a look at some alternative clustered key-value stores, like Project Voldemort, SimpleDB and HBase.