The feature I found most useful was the spam deterrent. You can use username+websitename@gmail.com as your email address. Then when the times comes you can unsubscribe from those specific emails or track which sites are distributing your email address to other spammers.

I already knew the other tip, but it’s pretty cool. You receive Gmail messages even it it’s sent to a slightly wrong email address address. For example, your email address is John.Smith@gmail.com, you will still get email when email is sent to JohnSmith@gmail.com or J.ohnSmith@gmail.com, etc.

Check out the article at makeuseof.com for more examples.