Actually, they do have obligation, legally, to their users. We all know they can comply to DMCA takedown notices to gain legal protection. However, to gain legal protection from their users , MySpace would be required to put the content back up if a user contests a takedown, and then be able to provide the issuer of the takedown notice with that user's contact information.
Specifically: "OCILLA (the part of the DMCA dealing with takedowns) also includes a counternotification provision that offers OSPs a safe harbor from liability to their users, if the material upon notice from such users claiming that the material in question is not, in fact, infringing."
Q: How many IBM CPU's does it take to execute a job? A: Four; three to hold it down, and one to rip its head off.