This is actually a significant release for Riak. Something that has always been sited as lacking in Riak was it's ability to index documents similar to couch. With this release, http://bitbucket.org/basho/riak_search/src (beta), what they have done is integrate lucene indexing on top of their distribution mechanism.
Besides that big news, this release intriduces a number of performance enhancements over it's predecessor. Read all about it, http://bitbucket.org/basho/riak/src/tip/releasenotes/riak-0.....