encryption-on-demand: for occasional private communication.

Most of us don't install, don't bother, don't like the tedium of encryption packages, with all that key management that comes with it. And for good reason, 99% of our email stuff is innocuous. No big secrets there. But on occasion we need to pass along a password, an account number, a romantic confession perhaps, and other confidential matters. This need has been recently addressed by the YouDeny.com site that offers ad-hoc, use-and-discard encryption solution, and it's free. They also claim deniability, which means the writer can claim his encrypted message is other than what it really is. Is this a useful solution for the occasional need for private communication? Would anyone try it, and write a report?