Heya, just throwing out my personal experience here with Vista after having it for about a month now. I installed Vista Business edition onto a new system after replacing my old motherboard, hard drives, video, and RAM.
First, in regards to the UAC security feature it does not prompt you on every single little thing you do, that is false. Normally the UAC appears for me during one of two things: when installing new software it prompts to verify I want to install something and also when I try to access system utilities that will be interacting directly with the OS DLLs or kernel (for example, various administration tools).
When I am browsing the 'Net or running a game I don't see the UAC at all. Some might see the UAC thing as a hassle and a waste of time but my thought on this -- for what its worth -- is that this is a new Microsoft product which is normally a touchy thing especially in regards to security. So, something like the UAC isn't too bad of an idea if it will help prevent malware or trojans from being allowed to automatically install themselves onto a Windows system.
It can also be bypassed or turned off completely via Local Security Policies but I'm a bit hesitant to do that, again because this is a new Microsoft product.
I did have problems running the C&C3 demo but this was fixed by installing the DirectX 9.0c program files. The demo wanted some DX9 files that Vista obviously doesn't have but by instaling DX9 the game then worked without any further errors or prblems.
The other few games I play right now like EQ2 and Defcon show no signs of problems while playing either. I tested Doom 3 as well and that ran good too.
As far as the Aero interface and gadgets I kind of like them despite the extra overhead they add to memory. Right now when I run the Aero desktop and gadgets that eats up another 50-60 Megs of RAM. When idle, my PC averages a usage of about 500Megs of RAM (that includes a/v software running the background, the various gadgets I have and other startup programs). Of course, the way Vista handles RAM and the way XP handles it are quite a bit different which might explain why it even uses that much RAM.
Now, I'm not saying everyone should get Vista right away. Far from it. If you have XP there's really no reason to get it unless you just absolutely have to have the newest thing and you just absolutely want to try things like ReadyBoost or Speedboost that come with Vista.
But for somone like me who was running Windows 2000 and was building a new PC, Vista might be worth your time to check out.