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.
Do I really need "Old Snakey," essentially an version of Tetris from way back when? Probably not. Of course, I enabled it.
Pictures in chat may be a nice feature. Enabled that too.
And then there are things like fixed width fonts, keyboard shortcuts and rating systems that may be handy.
The big picture seems to be this: If these features are any indication Google may take Gmail into a more social directions. As these experiments roll out don't be surprised if you find a few that are designed to keep you in Gmail a bit longer.