DeluTube, as its name implies, can serve up some video clips even after YouTube has purged them. That includes clips that contain copyrighted music and many clips that aren't work safe. Delutube allows visitors to enter the video ID (pulled from the end of the YouTube URL) of a deleted clip, then attempts to retrieve the clip from YouTube's system. Clips are apparently not deleted from YouTube's database at the moment they are taken down (or they at least persist in YouTube's cache before being cleared), allowing DeluTube a chance of retrieving them. The site also allows for the easy downloading of the clips.
DeluTube isn't the only service that can do such a thing, of course, but it's possibly the most ironic; the site makes money serving Google ads. The creation of these services shows how much demand exists for this sort of material, and what a hard time content owners have controlling it. The line of legality is very fuzzy since the clips all come from YouTube's servers, whether they infringe on copyright laws or are simply inappropriate. Lawsuits are undoubtedly coming, but will they target YouTube for not completely removing the videos or will they target DeluTube and other sites like it?
News source: Ars Technica