Google has introduced OAuth authorization for Gmail, meaning that approved applications can access your Gmail account without you giving them access to your Gmail username and password.
OAuth has been used as Flickr and Twitter for some time, but is a new development for Google.
Previously, if you wanted to get push notifications on your iPhone when you received a message at Gmail, you had two options: trust a third-party application with your username and password, or automatically forward a copy of all of your email to a different email address and trust that they would not save a copy of your email. As you can imagine, neither of those made security-conscious users very comfortable.
There is already an iPhone app available which uses OAuth, SmartPush ($2.99) by Syphir promises to give you finer control over notifications from Gmail on your iPhone. We hope to have a review of SmartPush here on TUAW in the near future, so stay tuned for that.