Well to make this post short, yes, is worth it. C’mon is 20 bucks, the installation takes like 40 minutes and you get some new iOS features for OSX. From now on is OSX, no more Mac OSX by the way. Really nice notification center, iMessage (which can be integrated with gmail chat), GameCenter, AirPlay (really improved), a better Safari with some cool features like sharing and iCloud Tabs, iCloud for iWork in your iOS and OSX, some stability improves, speed, etc.
In a few words is an updated Lion, more fast and with more functions. To update just downloaded from the Mac App Store and click three times on the installer. Wait for about 40 minutes and that’s it, you are done. Your data will be intact, you will not lose one single byte of information.
Is simple, is fast, is cheap and is a pretty nice upgrade to Lion. If you love iOS games they will be launched in OSX and you can even use your iDevice to control the game (like in Real Racing 2 for Mac for example) or connect your xbox 360 controller or gamepad to control the game the way you love it.