Should we have tags for different tool kits (especially gtk and qt)? Often, different users (mostly on Linux) will want software that fits in with their desktop. Also windows users may want native toolkits instead of Tk. Is it worth having tags for that?
If the question is about these toolkits specfically, then these tag are appropriate.
But if you're trying to slice up the site into much larger swaths ("the stuff I'm interested in versus stuff I'm not"), then tags do not work very well for that purpose.
Let me put this into a different context:
In the early days of our Cooking site, a user suggested we label every question that didn't have meat as an ingredient as vegetarian. It wasn't that they wanted a tag for questions about vegetarianism specifically. They simply wanted a way to divvy up the site between questions a vegetarian might find palatable and those they don't.
I hope I'm understanding the crux of your question.