Spiral Frog will be offering free music in exchange for one of your most valuable assets. You give them some of your time and attention by watching their advertising and they will let you download music to your computer for free.
No doubt, there will be some people who would be willing to watch an advert and then download a song. If the press is to be believed, those same people are going to be disappointed on two counts.
The first indignity is that the songs will play only on your PC. The digital rights management (read copy protection) scheme built into the songs will keep them from playing on portable music players. Secondly, the only way to keep the songs into the future will be to go back to the website and watch more ads. If you don't take your ads on a regular basis, the songs will self-destruct.
qv: Spiral Frog