most new games are multi threaded, some old ones every preform better (ut 2004 has "coarse" threading an sees a minor increase with DC). Personally I want to go quad core, as a linux/wintendo user I see the need for more 4 cores, but not 8. Source engine, ut3 engine, doom3 engine are all multi thread, or soon to be multi thread. Valve promised us q1 2007, but it looks like summer now, stupid of them to not program for the future. Oblivion is multi threaded, and a few other games are as well. The main this is that source seems to be the only time dual core/ dual gfx card actually takes away from performance. Other engines seem to see no performance boosts but don't actually get harmed by it.
you would be foolish not go conroe over an fx57!