Apparently this "investigation" of megaupload has been going on for two years, so it's not like they just decided to shut them down now. This also has absolutely nothing to do with the recent SOPA/PIPA development and protests, it's just a coinciding event that would have happened regardless.
Though, I don't understand how it could take a whole two years for them to get a site like that shut down.
But whatever, there are a lot of sites like megaupload out there which I'm sure everyone will flock to now. It's just, a lot of websites that relied on megaupload will just have a lot of links to fix, that's all.