I will never understand why people believe Snapchat when they say the photos would disappear after a set time. Nothing digital ever really disappears. It is long known that deleting a file on your PC does not eliminate it. It is also known that the entire Internet Protocal (IP) is based on replication--copies of the same file can be found on a lot of servers.
My colleague showed me this Valleywag post in which they dug through Snapchat's "law enforcement guide". What did they find?
Since Snapchat is a mobile application, they are able to tie each photo to you personally, they have your telephone number, email and username (through the carrier). This is more than sufficient to identify you, your name, and go to any data vendor or credit report bureau to take everything else. Wait, the company keeps "a log of the last 200 snaps that have been sent and received."
Like Eric Schmidt said, you really shouldn't be doing things you don't want other people to know about.