Grooveshark has had[0] a very sharp HTML5 interface for several months now. Here's a story[1] on HN from 220 days ago with discussion about it. Pandora is very late to the game.

[0] http://m.lifehacker.com/5705712/grooveshark-pushes-out-a-new...

[1] http://news.ycombinator.com/item?id=1968362