Just a heads up if you are looking to dive right in: The client libraries still lag behind Riak itself, so it might be a while before you get all the goodness unless you plan to roll your own.
Yup. For haskell users, I have a trivial fork of Mailrank's riak-haskell-client that is tested to work with riak-1.0rc1; I haven't tried the secondary indices stuff yet, but it's possible that it would work too. It's at https://github.com/tsuraan/riak-haskell-client for anybody who wants to try it out.
I checked the protobuf spec, though, and Riak 1.0 is completely compatible with the older client libraries. All the changes are backward compatible. So you get perhaps 90% of the new hotness.