Secret gmail feature #1: you can add and remove periods from your username with no change in mail routing. There is no collision with other accounts since only one account (stripped of periods) is allowed to exist. So firstname.lastname@example.org is the same as email@example.com.
Secret gmail feature #2: you can append a plus and any string to your account name and it will still be routed to you. Try creating filters by giving out your address this way: eg firstname.lastname@example.org will be delivered to username ‘example’ and email@example.com will be delivered to firstname.lastname@example.org.