Runar Jordahl implemented a Riak Interface for Pharo Smalltalk. Why is this interesting, you may ask.
Runars Interface runs in Pharo 1.1., uses the ZincHTTP components and is currently in beta. Check out the included test case "EpigentRiakRestConnectionTest" to see how easy you can use it.
You have to set up a riak running at "http://riaktest:8098/riak" if you want to try.
I hope to find the time to play with this a little bit more.