I was looking for a way of using the same email for multiple twitter accounts and found a link which explained that google email considers firstname.lastname@example.org and email@example.com as the same address.
Straight away that gives you a two for one deal on your google email. It doesn't end there. Google email addresses also ignore dots (.) when emails are sent to them. So firstname.lastname@example.org is considered the same as email@example.com. So all variations will end up in the same google mailbox
There are many applications for this feature including spam control however for me it makes it a lot simpler when signing up for web applications like twitter where your email address has to be unique for each account.
Hope this helps someone.