OK, I've been away and this is old-ish news. Project Playlist is now on the receiving end of a lawsuit initiated by 9 record labels brought together by the RIAA, sending out a notice that they don't like PP's contributions to the world of copyright infringement.
Odds are, this is just the first step to making PP into a legal site, but, maybe not, maybe PP could make a semi convincing case for, or at least maybe they think they have a case. It's known that they have been talking to the major labels, and not everyone is suing them, sony is a notable exception.
Here's how I see it playing out, Sony will force PP to use their newly acquired audio filtering technology (from Gracenote) to ensure that unlicensed music does not appear on the site, and in return it'll license its catalog on similar terms to those agreed to by other ad supported sites like imeem/last.fm. Over time other labels will follow, but many of the users will jump ship in this period when they find their music options limited. Some will go to imeem with it's more complete catalog and embeddable player, others might try to stay ahead of the legal stormfront and move to muxtape where pre-release tunes and the beatles are still not blocked.
In the end PP will join imeem and last.fm as a legal site, it'll probably lose a lot of users during the transition to legality, so imeem will probably re-establish its top position in the US, leaving PP as the 2nd ranked site in the US and 3rd worldwide. And to pay for all those plays it'll start to host millions of ads, but that will mainly be a cosmetic change to the site, on the back end of things I predict that PP will start serving its own content once it gets licenses, while they might get some legal deal that protects their right to manipulate and serve references to other files, those other sites which are hosting the files will still have no such right.
So changes are a coming.
Maybe a lawsuit will still happen, but I doubt it, PP launched very soon after imeem's embedded playlists got popular, their implementation was designed to save them money on server costs and limit their legal liability, but I believe they want to become a legal site and there wont's be any drawn out legal proceedings.
If you're looking for a lawsuit, I believe seeqpod is the place you should be looking.