Hi all looking out for making a forum for your site..
this is one of the methods which i have implemented on www.pleasecoumtnein.org
Act_As_threaded which is a tree structure forum where performance is a concern. The nested_set model is insert/update heavy but the whole tree can be retrieved in order from the database with a single query.
It can be downloaded from http://i.nfectio.us/plugins/acts_as_threaded.zip
More in depth execution and implementation will be shown here later on.