Google has introduced a very interesting new feature, 'login by QR code,' which makes it safer to log into your Google account on a foreign computer. There aren't many use cases for the feature, but you'll be glad it exists when you actually need it.
Visiting accounts.google.com/sesame will generate a QR code which you can then use on your phone to log into your account in the browser you used to generate the code.
UPDATE: The page no longer works. Google deemed it experimental and has now shut it down. You can read a more detailed explanation here.
You scan that code with your phone and you'll be taken to the Google login page or to a page asking you for authorization if you're already logged into your Google account in your phone's mobile browser.
If you decide to authorize the access, you can choose between opening Gmail or iGoogle in the desktop browser, where you generated the QR code. You will be logged in and the desktop browser will then be redirected to the page you selected.
It comes in handy when you don't feel safe in typing your password on that computer, or tablet or phone for that matter, fearing keyloggers or something similar.
It's also useful if you don't remember your password, for example, if you normally use a password manager, but you have it remembered in your phone's browser.
There are a couple of safety features, since the feature provides access to your account. For one, the mobile page warns you very clearly that you're about to authorize another computer to access your account and that you should only proceed if you actually intended to do this.
The QR code link also expires after a few minutes. This means that you may have to refresh the page and get a new QR code if you're not already logged in on your phone, especially if you're using 2-step authentication.
It's not clear when Google introduced the new feature, it appears to be a new page. If it isn't, Google has done a pretty good job hiding it from users. It should work on any phone or any device capable of scanning and parsing a QR code since it's a simple web page. It has been tested successfully on Android, iOS and Windows Phone 7.