Actually, all gmail accounts have near infinite emails built in. If your gmail address was [email protected] then [email protected] would get to you without any config and indeed if you had a Marriott label I think it might auto-filter into it. In addition to being able to tack on +whatever you can also insert "."s wherever you like, just not more than 1 at a time. So [email protected] will also get delivered to the the [email protected] account.

Alas a fair few websites are poorly coded and can't cope with a + in the userpart (bit before the @) in email addresses even though it's totally valid. Worse are sites that can cope with it in some places (like sign up) but not others (like unsubscribing from their mailing list).