I hate to say it, but I'd try to find a new domain if possible. With domain hacks like this, They feel a bit dated, but worse, I never remember where the splits are.

Sec.ret.ly? Se.cret.ly? S.ecret.ly?

Also, how big is the use case? I don't think one load URLs are something I'd ever really want. What if they accidentily closed it?

And it doesn't prevent sharing, since they could just save it and re-upload.. Basically, either I trust them, or I don't. I don't see where a one-use URL helps.

I think the best use-case is when you're chatting with someone and want to quickly send them something you wouldn't want to send unencrypted. A password or some image of a prototype. Instead of posting it to a public site and just waiting to delete the image, or text.

As for the domain, my goal was to keep it as short as possible. The root domain cret.ly works as well so I could just downplay the "se." to prevent confusion.