I use SOLR for searching through millions of videos and products. I've found that combining SOLR with a traditional RDBMS and a column-oriented DB such as HBASE or Cassandra is really the way to go.
I mostly try to add helpful tips and links to the pages in a hope that others will find this wiki to be more useful. You can contact me over AIM using the username here. I also have a yahoo email account with the same username.