Building a GUI Toolkit

[Tim Diels]

Hi

I was thinking of writing a GUI toolkit from scratch using a basic '2D 
library'. I have already come across the Widget Construction Kit.

My main question is: Could I build a GUI toolkit of reasonable 
performance with the Widget Construction Kit, would it still feel more 
or less lightweight? By reasonable I mean that the user wouldn't think 
of the interface as being slow or unresponsive.

I've also thought of using pyglet to build widgets with, but this would 
seem to be overkill. As a side question: by using opengl, the work would 
be delegated to the GPU rather than the CPU; is this always a good 
thing, or does it have downsides as well (performance, power usage, ...)?

Are there any other libraries that may be of interest to me?

Thanks in advance