It looks like digital music has almost come full circle from the original Napster to Napster.com (limited free listens) and now to SpiralFrog, which will trade rights-managed music for your ad time. This notion of “paying” people to watch commercials online goes back at least as far as CyberGold, but SpiralFrog has potential because of the emotional value of music can be higher than its monetary value. The devil will be in the details for this one; much will depend on SpiralFrog’s catalog, but Universal Music Group has apparently signed on.