There is an alternative which offers all the community sharing aspects of Youtube but with increased quality. Not only that it supports HD. Upload a 1280x720 clip and Vimeo will auto create a small version (400x300) and allow viewers to watch the full HD footage. Here's Vimeos HD FAQ which explains more.
Users have the option of turning off HD at any time and load the smaller clip so bandwidth is not an issue.
Here's a comparison of a clips from Youtube and clips from Vimeo.
Note: Sadly Vimeo clips embedded aren't viewable in HD. Check their HD channel to view them in HD. Interesting fact: Vimeo was founded before Youtube. Just shows you don't need to be first to market or better. Just smarter.