Gmail trick for use one id as many . . .

Lets say your gmail id is : YourGmailID@gmail.com
Now any mail sent to following will go in your inbox.
You.r.g.m.ailid@gmail.com (you can use as much DOTS as you wish to and at any location within this id before @ sign)
YourGmailID+321@gmail.com (any number can be used between + and @)

Means your one Gmail account acts as millions of gmail accounts.
People creating account on twitter, FB or any other forum can register using these ids and verification email will hit one gmail inbox.

by the way

you can also replace @gmail.com with @googlemail.com
and with this one the dots and the numbers will still work and all emails will hit to your real gmail account.