Facebook ditches Cassandra for HBase
Cassandra is an open source distributed database implementation that started life at Facebook as a solution to their message inbox search and storage. Facebook announced the next generation of messaging this week, and it's powered by HBase.
Highscalability.com have a good article about the announcement and technicalities generally. I was particularly interested having recently read Bradford's comparison of the two.
What I take from this is a firm reminder that different NoSQL solutions have different engineering trade-offs, and that picking the right tool for any one application is more important that brand loyalty.