Reminds me of a time I had to call a company about an order of hardware parts and they wanted my credit card details over the phone. Having worked in telecoms in the past (on carrier server software), this isn't something I like doing, so instead I gave them a URL to a https page containing the details they needed. It also self destructed so you could only view it once.

A general purpose email version of this (both with and without self destruct (which should have options such as timer, N views etc)) would be awesome, especially if it automatically intercepted emails and moved them there. Would have to be something I can host myself, of course.