If you guys sign up with +hn within your email, we'll make sure to give you access right away.
Your product is slick. I can see myself convincing a customer to use this, which is not something I could say for Dropbox.
I don't see anywhere that myaddress@email.com and myaddress#this@email.com must send to the same mailbox. I only see that an address must "[contain] a locally interpreted string followed by the at-sign character."
Of course, this means that you can use - or ~ or # in your address but they don't have to be treated (and probably aren't) treated as the same address by most email systems.