I've been telling people for quite some time to make their own custom widgets, on a sub-classed Zinc object. As a matter of fact, I advocate using the Tk Zinc Canvas as the basis for a whole new GUI language, with all sorts of custom looking buttons, and rounded shapes, all prebuilt as Zinc-only widgets. There is nothing stopping you from doing that right now. There are other advantages besides OpenGL color gradients, bezier curves, and transparencies. The Canvas and Zinc are very good at handling their memory, so you can do alot of "creating-destroying" without gaining memory in your apps.

BUT it isn't 3d, and people will not write for OpenGL until all computers support it. Most don't, and even those that do, there are enough inconsistencies, that people avoid it.

Why do you think that you see very few OpenGL apps in wide use? Why are there almost no 3d applications in wide use on desktops? It just isn't time yet, because considering the power of the average computer out there, things are peppier and easier to write without it. Eye candy is great for the salesroom, but when people get it home, and run it day-to-day, they want it simple and fast.

There are some great examples in the Tk::Zinc demo, like the #7 in The Use of OpenGL( but they don't require OpenGL to run)