Tired of those tiny video offerings on YouTube? 320x240 video at 15 frames per second is starting to look a bit tired on large screen resolutions. At work I'm lucky enough to have a new iMac with a 24" screen running at 1920x1200, and trust me, YouTube starts to look a little... inadequate... on my screen.
Vimeo, an alternative to YouTube, has always offered, IMHO, better quality videos (they've been 460px wide and seem to be encoded at a higher bit rate). A few days ago, they announced the introduction of HD (720p).
To find out why this is a Good Thing, this example sums it all up rather simply (then view it directly on the Vimeo page, and switch to full screen):
At the time of writing the Vimeo website is running a little slower (why on earth might that be, hmm?) than usual, but run some of the movies full screen to see the difference this makes.