Can you honestly rule out the possibility that your experiences with Vista are either coloured by your disappointment with the OS? Can you rule that you're treating it like it's XP?

I don't want to get too deep into the technicality of advances made in Vista, but if we talk about Windows responsiveness, moving the UI from software to hardware rendering has pretty much eliminated visual lock-ups. Now, if you went in and disabled Aero, don't blame Vista if you lost all the advantages of the new composition engine. If we talk about application launch time, provided you don't get in an disable a lot of services and maintenance tasks, it actually improves over time by way of pre-fetch caching, until launching every day apps is practically instant.

TweakUI was a User Interface tweak program only. Considering the not less than significant shift in UI paradigm in Vista, very little of what's in TweakUI even applies to Vista. I have noted though, that when presented with a new OS, some people try to make it look like their old OS, usually by turning off new features. In the process, they do even really try to learn how to use the new interface.

Compared to other operating systems, like Linux distributions for example, Microsoft OS' provide hardly any customisation options at all. Instead, they invest huge volumes of cash into investigating how people use the OS, and try their best to make its behaviour and interface as transparent as possible. That's they way most people want it, boot up, play, browse, watch, then shut down. Heck, most people rarely venture outside the start menu. If you're spending a lot of time trying to manipulate Windows into behaving the way you think it should, maybe you should be looking at Linux.

Even if we take Vista performance now out of the question, XP puts an upgrade cap on a system. The standard lift of a machine is 3 years+ for your average user. During that time, they may upgrade the RAM several times, possibly the CPU and probably the graphics card. XP has a practical limit of 4 GB of RAM, will not support emerging technologies like DirectX 10 and will not be the prefered development/support platform going forward.

I'm not opposed to making recommendations, but it need be rational. Warn people what they're getting in to, explain what they need to watch out for; that's reasonable. Making blanket statements is not.