plus addressing, as another poster mentioned, but quite a few web forms trip up on that (will tell you the address isn't valid or give some other error), so another quick and easy but perhaps little-known trick is that in Gmail (and only gmail as far as I know) the period character is basically ignored in terms of username uniqueness.
In other words, taking your examples, without having to do anything extra or set anything up beforehand, emails sent to:
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
(and so on, for each permutation of where you put the dots)
will all arrive at the same mailbox, and you'll be able to create custom filters and rules based on each unique 'to:' address.