1st - Great UI! Can't live without it! Well, wouldn't want to..
2nd - Read the FAQ, didn't find answer.
3rd - Searched this thread, didn't find answer.
Now that we got that out of the way, on to the issues..
Recently, MonkeyQuest started glitchin' fer no reason. (i.e. I click sometimes and can't expand /collapse quests for a zone). This is particularly bothersome cause I don't know a way to get to the normal quest window with MQ installed.
Next, I get buttons on the minimap, which I can't turn off. Most notably the MazzleUI and ItemRack buttons won't come off. This is very annoying as they seem to randomly rotate (when I next log in) if I move them out of the way.
Lastly, The button for the warlock's 'Flamestone?' (I never use it), shows up in the right upper corner. This isn't a big deal but it's annoying as the UI is very clean for the most part.
These are the issues I see as a Warlock using the UI. Except for the MonkeyQuest issue, the others are trivial. However not being able to get to your quests is a biggie. It may have something to do with other addons, I don't know but I'll try to find out...
Love the UI, except for the complexity of set up and trying to find a setting that is sometimes buried..
Keep up the great work!