It says that once the content is accessed, it vanishes. So, you can have a max 2 day expiration length, but as soon as someone follows the link, it's gone? It's not a bad idea, but it is prone to abuse. I could write a scraper app that would give me all of the active URLs and in doing so would delete any message attached to them. I personally wouldn't, because it doesn't serve much purpose, but if there were a malicious agent, it wouldn't take much to wreak havoc. It wouldn't even be a DDOS level attack, just a simple scraper using minimal resources.

Truly, though, I do like it. I just think that the automatic removal might be a risky feature.