One feature I recently learned about Gmail is that Gmail ignores dots in the e-mail address before the '@'.
For example, email@example.com can be written as John.Doe@gmail.com or even firstname.lastname@example.org. E-mail sent to these addresses will end up at email@example.com as if the dots were not there.
So if you registered with a dot in your Gmail username, you don't need to mention about the dot when handing it out.
Another tip I across in this article is that you can add a '+' after the username with any letters and Gmail ignores this also.
So let's say one would like to join several services that require its e-mail address, that person could use firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, etc. where all incoming e-mails land at email@example.com.
Of course another option is to vary the dots, e.g. firstname.lastname@example.org for one service, email@example.com for the next and so on. This could be useful for services that don't allow a '+' in the e-mail address.
If spam starts coming in, then it's just a matter of checking the 'To' field to see what e-mail variation the spam was sent to, which in turn can be paired with the culprit who sold the e-mail address.