Egg gone bad?

A friend of mine called the other day and asked how to know if an egg is not okay to eat anymore. We had both heard different things about expiration dates on the egg packages so I found this tip on ehow.com .

Basically you float an egg in water in a bowl and look to see if it stays on its side or floats to the top. This site states that a fresh egg will stay on its side at the bottom of the bowl. But if it floats...well toss it! Somewhere in between - it's up to you.