And neither does a lot of proprietary technology. But the possibility that ads will show up on either type of technology is obviously very different.

Now, we are about to see add supported P2P services.

At the Midem conference in Cannes, France, Qtrax and its parent company Brilliant Technologies Corp. announced deals on Sunday with all four major labels that would make it the first free and legal ad-supported P2P service with major label music.

By allowing users to share DRM-protected files with label approval, Qtrax CEO Allan Klepfisz said he expected the service to offer over 25 million songs, dwarfing the catalogs of iTunes and other online music stores. The service launched today, after what Klepfisz called four and a half years of negotiations with the labels.

…As with other free, ad-supported services, revenue comes from advertisers who want to target ads to specific types of listeners.

[source]