I have read quite some things on the different larger key-value stores, especially on how they scale. And what I have seen I really like Riak as well. However, we have been setting it up over the last few weeks, and sofar it's less stable than I have hoped/expected: we have had nodes crash for no apparent reason. I hope we can resolve them, as I really like the model, especially the horizontal scaling, but it must be stable to use...
There are worse things than crashing. Like soldiering on and corrupting data.
The most unstable clustered database I have ever come across was suffering from broken TCP drivers. Never assume a cause until you have actually tracked it down.
I agree with itaborai83 that individual node crashes shouldn't be as big deal with the consistency model and redundancy offered by Riak. That is one reason you might go with Riak over something that offers stronger consistency, but is more picky about node crashes and recovery.
but aren't nodes supposed to crash, albeit in a tolerable way? Even though I conceptually like Riak I haven't tried it yet, because the problems that I deal with aren't worth the trouble of setting up a cluster and managing it.
I think that the cluster is supposed to be stable. The nodes, not so much.
I've never had Riak crash on me. If you are having trouble ask any of the Riak guys and they will bend over backwards to help you. If you have found a crasher bug, I bet they want it fixed more than you do.