I haven't used Datomic at all myself, though I was at this event and I found it very appealing. The issue of having an easy audit trail is absolutely critical

I haven't used Datomic at all myself, though I was at this event and I found it very appealing. The issue of having an easy audit trail is absolutely critical for many businesses, and is ill-served by most existing databases. This is one thing I liked about CouchDB - CouchDB does not enforce this strictly, the way Datomic does, but the model encourages "append to edit" rather than strict modification. I haven't had the time yet, but I'm excited to check out Datomic specifically for this reason.