How can MediaFire (and other online storage websites) afford to offer unlimited storage space, as well as unlimited bandwidth?
I gather that they basically work on the principal that:
They're basically taking a gamble on the above statements..
A lot of their bandwidth will be provided with interesting peering arrangements, as well as a few transit providers.
Storage is also cheap, and becoming cheaper, as long as speed and performance isn't a real problem. Caching data will help alleviate any real disk slowness, so it's not as noticable that they're using 5400 rpm disks, not FC connected disk arrays.