I think CouchDB is vastly underrated as a hacker database for toy projects. We're talking about an incredibly simple database, with powerful replication abilities, with brain-dead administration, and one-click offsite backup and synchronization, that requires no real client libraries to work with. It makes it comically easy for me to hack on toy projects on the road, then sync them right back up afterwards when I'm done.
I know CouchDB sometimes gets some flak for not performing as well as other NoSQLs. Anecdotally, that feels as if it's gotten a lot better over time, and this BigCouch merge may improve things further, but sometimes there's a case to be made for using something just because it's fun and easy to work with.