I haven't used Riak, but I did look into it for a project short while back. One problem I had was that the documentation on their website is heavily focused on

I haven't used Riak, but I did look into it for a project short while back. One problem I had was that the documentation on their website is heavily focused on what Riak is, vs how to use it. It's great that you can get such a fundamental understanding of Riak as-a-dynamo-implementation, and they do a great job writing that stuff, but its completely out of touch with what I expected/needed. Technically, what eventually put me off, is that I couldn't figure out how to maintain a clean secondary index. If you have a: SiteId, UserId, Data, and you want data to be accessible by SiteId or SiteId+UserId, I couldn't figure out a nice atomic way to maintain the secondary index. This is pretty basic stuff. I'm glad to see 1.0 will support native secondary indexes, but I think my inability to figure it out shows that their documentation is poor (or it could be that I suck).