Earlier quoted context omitted.
I emailed that question and a few others (ie- handling disconnections). Shall update when I get a reply (if not already). :)
The reply. Not exactly the answers I expected... [Q: How do you stop a download link from being shared?] A: We don't. We bet on the god will of mankind. [Q: Are links screened for copyrights, fakes, etc?] A: No. Gumroad isn't a marketplace so we don't need to do this as much as others do. [Q: How are disconnected downloads handled?] A: Working on improving this. We do OK.
It's pretty scary considering what just happened to Megaupload. I suppose one could implement some sort of community-driven screening process for sellers.
Thanks for posting this!