I don't think cbs will kill last.fm, not shure what they can offer exept cash. But they are not giving away $280 million for sure..
Last.fm needs to make some heavy deals to grow and evolve, they still have a great potential, this should give them muscles.
With this deal the RIAA and their lawyers will smell the cash and come hunting for it. They are as usual the biggest threat. In their crusade to kill internet radio (or radio that doesnt suck), Last.fm could be next.