Yes, but...
So there may be paedophiles operating on Myspace and it would help law enforcement agencies protect our children if Myspace turned over their data to them.
Great, after all, who could argue against something to protect children?
Except witchhunts like Operation Ore comes to mind. What happens if (when!) someone is falsely "identified" because they have the same name as a genuine offender or they're a victim if ID theft or simple human error?
And then what follows? Will the Department of Homeland Security start demanding information "just in case there's any terror suspects using Myspace to plan attacks"? Or people just expressing "Un-American sympathies"?
This sounds to me like another data mining/ fishing expedition by those who think the best way to "protect" our liberties is by knowing everything there is to know about us and ignoring that fundamental liberty called "Presumed innocent unless proven guilty"...