I see Rafe Needleman is reporting that YouTube are going to start streaming video in hi-def imminently.
According to Needleman:
YouTube co-founder Steve Chen, speaking at the NewTeeVee Live conference today, confirmed that high-quality YouTube video streams are coming soon…. the service is testing a player that detects the speed of the viewer’s Net connection and serves up higher-quality video if they want it.
Chen also confirmed that YouTube stores the native quality of the originally uploaded video – this is no surprise to iPhone or iPod Touch owners who have a hi-def YouTube service already.