I've been using Vista for quite a while now and the security is much, much better than it is in XP (primarily due to User Account Control and IE Protected Mode).
The boost that you'll see for gaming will revolve around 2 things:
1) The improvements to the OS, like DX10
2) The improved hardware needed to run Vista effectively.
As for being "bug-free" - if it was bug free it wouldn't still be in beta! But RC2 is stable enough for me to use as my primary OS - so I'm figuring that it's getting pretty close to release.
The decision to upgrade is a personal one. If you're more than just an average user (being on the forums means that you are), then it comes down to what you want.
Do you want to be on the cutting edge of technology? Then Vista and it's hardware requirements will put you there (I'm building a new system just for this purpose).
But, can you afford all the new hardware? Vista isn't a quantum leap in performance by itself. You'll see performance increases that are due more to the hardware than to the OS itself.
FWIW, IMO if you're fairly knowledgable with XP, don't have a bunch of money, and don't have a specific need for Vista (ie - I need it so that I can support others when they encounter problems) - then stick with XP until the prices come down.
Finally, Vista is being pushed out the door. They've dropped features from it to meet the deadlines. So, I'd expect Service Packs to come out as things are developed. One of the things that I'm looking forward to is the development of the WinFS file system. Also, I'd expect less in the way of Security fixes just because of the way that Vista runs.