Yes. Check out Marco Arment's preview.fm. He had a similar web app that allows you to preview album.
Oh yeah, I've heard about it before. I will definitely implement it using <audio> if it doesn't heavily affect loadtime.
It shouldn't affect load time at all. Don't load the preview until the user requests it. That's the one feature I thought was missing. Otherwise, it would be awesome. I mainly use iTunes to listen to preview, removing the step to go to iTunes for that would be awesome! :)
Definitely man! That feature will be quite useful.