Pastebin for binary files? By the look of things, clean and easy to use? Handy!
It's probably time to start thinking about ways to monetise this to pay for the hosting costs at least.
Also, have you talked to a lawyer yet? If this takes off and you keep it up long enough, inevitably you're going to get people using it for child porn, stolen credit card numbers, leaked classified documents, instructions on how to make home-made bombs etc and someday a relevant law enforcement agency is going to want to have a conversation about the content that Mr Smith sent to Mr Jones via your server. It's probably a good idea to get your legal position straight before that day rather than trying to do it after the fact. And yes, I do recommend talking to an actual lawyer. Internet commentary is not an adequate substitute for legal advice here.
Seems like a lot of the issues are mitigated by the file going away after the first download. Especially if there really are no logs or anything at that point.
I am not a lawyer™ but the creators should definitely consult one to 1) determine how much risk they are exposing themselves to and 2) determine a reasonable course of action to limit that risk exposure. The question is not on whether or not we believe something to be "legal" or "illegal" but whether or not some part of their service might draw the attention of a group large and angry enough that might try to make them prove something in front of a judge. This is the real danger to a small group of developers: the RIAA has many lawyers on retainer while the upfront cost of dealing with a lawsuit would bankrupt most individual developers.
It's probably time to start thinking about ways to monetise this to pay for the hosting costs at least.
Also, have you talked to a lawyer yet? If this takes off and you keep it up long enough, inevitably you're going to get people using it for child porn, stolen credit card numbers, leaked classified documents, instructions on how to make home-made bombs etc and someday a relevant law enforcement agency is going to want to have a conversation about the content that Mr Smith sent to Mr Jones via your server. It's probably a good idea to get your legal position straight before that day rather than trying to do it after the fact. And yes, I do recommend talking to an actual lawyer. Internet commentary is not an adequate substitute for legal advice here.