First thing I would do is switch over to Python. That way you can start using PyQt and really dig into Qt.
(Also I love python…so I could spout off another gajilion reasons to change)
If you stay using Mel with Qt, you’re sort of constrained to the Qt Designer features(which are pretty solid actually)
I started learning PyQt on the job at RnH making UI’s for my distributed tools. Unfortunately the UI for Qt Designer ironically doesn’t work at work, so I forced myself to learn
http://zetcode.com/tutorials/pyqt4/
These ^ were a great help in getting started, as well as searching through here and stackoverflow. I would also suggest Nathan Hornes blog and joining the python maya google group.
You can also convert Qt Designer ui files to PyQt classes and learn like that too.
Really PyQt isn’t that different from using regular MEL UI’s/cmds ui’s other than the initialization process/parenting. But it gives you soooo much more control over how things are viewed.