What about fiber optics b/c they have unlimited potential, and a shitload of ram. Also, many tasks such as 3d rendering don't require high bandwith at all. I'm not sure how practical it'd be though- how many home users actually push a comp to its limit?
Flame, Beowulf clusters need to have programs written explicitly to be broken into segments (like distributed computing). I don't see any way to get around that. Not a huge deal, but I don't see any reason right away why several computers with an expensive connection and new software would be easier than further developing stand-alone computers.