Muxtape, Mixwit and the RIAA

OK, how is this NOT copyright infringement? Checkout http://muxtape.com/ and http://www.mixwit.com/. Cool idea, right? Share your mix tapes? You can try to rely on the DMCA, but if they're betting the farm on that they better read Grokster again. See http://www.keepandshare.com/doc/view.php?id=488991&da=y
I will bet that RIAA will commence legal action against one or both within three months. Watch this space for updates.