haha! Thanks! We recently switched from a hacked-version of sphinx to solr. We're using some custom solr features (including some that we're contributing back)

haha! Thanks! We recently switched from a hacked-version of sphinx to solr. We're using some custom solr features (including some that we're contributing back) but most of the speed comes from solr faceting. It wasn't trivial to setup though - Harish did a lot of work performance tuning solr.