Thanks for the interest.
First of all, I spend anywhere from 10-30 hours a week adding in features and bug fixes to QuickGUI.
Issues that are brought up on the forum are generally solved in short time. The library started in April, so it's really young in comparison to CEGUI. As for RBGUI, the library is a great starting point for a UI solution, but I don't think its maintained by the original author anymore. Not only that, but I have yet to see a unique skin with the library, I have a feeling its not as easy to skin as one would hope. So basically, CEGUI is my only competitor.. although it is a great competitor. Large user base (testers), lots of widgets, and the basics of a layout and skinset editor, make it tough to compare. What QuickGUI offers that CEGUI doesn't is: active development, ease of skinning, ease of use. Granted there are bugs like you say, but I'm usually quick at handling them.
Its true that QuickGUI's more complex widget set needs work, for example, I'm continously working towards a TextArea and MultiColumnList widget, but a lot of core design features keep showing up. I have not created a GUI library before, and as such, I'm always finding a better way to accomplish things.
Another appealing factor of QuickGUI in active development is that I am more capable of adding in features you want, especially if they benefit others.
What is the time frame of your project? I imagine QuickGUI should be getting decently stable within a months time.
DX vs. OpenGL: I haven't ran any performance tests, but I see OpenGL as only a little lower in FPS than DirectX. I ran VTune over the code a little while ago, but didn't find any obvious spots for optimization. I will probably analyze the code at a later date, to see any potential optimizations.
Portability Issues: What platform are you using? There are QuickGUI users on Linux, and some using Code Blocks IDE. Although I'm not familiar with these platforms myself, there are users available to help.
Console: That issue is already fixed in my code, but I'm working on something and can't commit at the moment. Normally I would just fix and commit immediately, but I'm working on some core features related to skinning. (fixes applied during the process, I fix bugs as soon as I can)
Hope that answered some of your questions!