Google has created Gmail Labs and invited its users to test out new features. In other words, you're a guinea pig of sorts.
The official word is that Google wants a way to screen the best ideas to add features and get Gmail out of beta--someday. According to Gmail product manager Keith Coleman:
Gmail Labs is a way for us to take lots of the ideas we wouldn't normally pick and let you all (who use Gmail) decide whether they're good or not. When you sign in, you'll see a new page in Settings called Labs. It has a list of experimental new features, and you can enable or disable each one. Some of the popular ones will become core parts of the product, and we'll eventually retire the ones that don't get much use. We've put feedback links in there, too, so you can discuss a feature with other users and the engineer(s) who wrote it.
Pretty neat eh? These features are obviously designed to make Gmail more than just an email system. You don't have to play along, but you probably will.