I'm using it. If you already have Vista then it's a definite yes. Surprisingly simple to migrate to since it keeps all settings and installed apps. I installed it by mounting it to the drive, completely CD-free installation.
Gaming performance; there are reports of improvements. My games ran fine on Vista anyway due to 6GB ram.
The main changes are the way the explorer works, the new taskbar (very much like apple dock) is very useful and intuitive. And, this might seem silly to some, but the desktop themes are sooo cool. I'm using the "UK" theme.
One other thing I like about it, but its quite a niché thing, is I am now running dual ATi and Nvidia cards. Cant do that on Vista. The Nvidia is my PhysX card, while the ATi is the main card.
The ease of upgrade from vista makes it feel like just installing a service pack, just a very big service pack.
And for the price - free for a year, it's defo worth it.