Was using sphinx + ultrasphinx, but was talking to Evan Weaver the other day and he mentioned thinking_sphinx is the one to use now since Pat Allan is really intensely working on it, so we switched over to that in this release.
Note: For larger production websites served off multiple app servers, thinking_sphinx doesn't work well since it tries to do reindexing of changed items directly within the rails process. However, there is a great fork of the latest plugin that can use updated_at, so you can index your deltas on a cronjob, offline. Check it out if you're going to use thinking sphinx: http://blog.edhickey.com/2008/09/15/thinkingsphinx-rails-plu...
