Every now and then somebody asks what is the direction Microsoft is going to with Avalon, ahem Windows Presentation Foundation (WPF), in respect to the UI consistency. The reason is mainly that of the few apps that Microsoft built using WPF (Sparkle and Max come to mind) none looks like a normal app on Windows XP (haven't tried them on Vista but judging from the beta releases till now, they are not looking “native” on Vista either).

Because WPF is so powerful and because many GUI effects are easy to achieve without a performance penalty it is very tempting to make your GUI stand out from the rest, consistency be damned. We are all guilty of this and it is hard to resist it. On the other hand, the cornerstone of the modern graphical OS is consistency so that users have to endure minimal if any training when moving from one app to another.

So what is one to do? Go with the crazy “skinnable everything” approach like Winamp or stick to the default OS look whenever appropriate? I'd say that we should definitely not underestimate users - judging by the number of Web apps that people feel comfortable with it's probably safe to assume that as long as UI follows some kind of logic, people will be able to figure it out. It's important to be internally consistent and to do the right thing. One of the most compelling things (to me at least) is the possibility to mix “classic” UI patterns with the “Web” UI patterns in WPF. A repository of UI patterns exists and is perfect for keeping things sane. I've bought the book and highly recommend it, even though there's not much there that you don't already know if you are an experienced GUI developer.

It's probably a good time to quote Spiderman (of all things): “With great power comes great responsibility”. Just because we can do almost anything with WPF doesn't mean we should. I'd say that making a great UI is becoming even more complicated, even if the result(s) on average will look much better than before.