I've spent the day trying to install erlang on OS Lion and also to install Riak Search - quite frustrating to say the least.

The installation instructions on the basho site don't seem to work as they link to a tar ball that doesn't seem to exist.

Here's how I managed to install RiakSearch on OS Lion:

$ curl -O http://downloads.basho.com/riak-search/riak-search-0.14/riak_search-0.14.0-osx-i386.tar.gz
$ tar xzvf riak_search-0.14.0-osx-i386.tar.gz

The tar ball is precompiled so you should be able to test if it worked simply by typing:

$ riak_search-0.14.0-osx-i386/bin/riaksearch start

Note - that the time of writing, the latest version is 0.14.0. You can check for the latest version by looking in the riak downloads directory

Hope that helps.