Wikipedia is just chock full of usefull tidbits.
For those of you who have been know to invoke the 5 second rule there comes this sage advice from Wikipedia:
The five-second rule is rarely applied to other people's food, although many instances have been documented.
If a food falls in feces, the five-second rule is never used.
The five-second rule was also featured in an episode of the Discovery Channel series MythBusters. The results they got from their tests confirmed Clarke’s findings: time was not a factor when food is exposed to bacteria; even two seconds' exposure is more than enough time to contaminate it.