Really, which? I have never come across a site using MegaUpload to host non-pirated content. Not one. single. time. I'd love to see some examples of this non-infringing usage. Surely you can find some via archive.org easily enough, if they're so common?
I've seen plenty. Mainly around gaming stuff like mods, or even smaller games where the developer released versions on MegaUpload or similar sites. The only specific examples I can think of off the top of my head are NSFW and I'd rather not link them here, but they definitely exist, and MegaUpload was always the easiest to use of the bunch.
FWIW, forum.xda-developers.com and phone modding forums like it often use cyberlocker services, usually for the same reason: you have a lot of folks who want a file, you don't want the forum software to have to deal with the traffic and you certainly don't want to have to email it to everyone who asks.
Cyberlocker services yes, but megaupload specically? When I've seen stuff like that used in actual communities it's been either stuff like dropbox links, MSN's one (SkyDrive, or LiveDrive, something like that?)
