there are lot of small things that are wrong and lot of users don't know that
u will be surprised of some things

on some services like 123greetings for example ( a bit popular service)
u wanna send a greeting to a some one they ask u to put ur mail, the recepient mail ....

well they never check if that is ur mail, so u can put [email protected] in ur mail
[email protected] and send a greeting saying u succeeded at s'cool

there are lot of uses like sending a mail from [email protected] to [email protected]

hehe immagine
they never check the id of the sender, they can not actually,and the recepient will get a normal greeting card saying someone has sent u a mail, real geek and funny

did u know that?
anybody got such stuff?
will be glad if they post it