I've been using NGUI for almost 5 months now and I have to say that it is a great tool.
Just a couple of things:
- Better sorting algorithm in BetterList, it does 3k+ comparison for 50 elements
- Fonts in general, we are building for mobiles, so dynamic fonts are not an option and bitmap fonts, even when pixel perfect & pre-multiplied alpha, they don't always look good and down-scaling is ugly. It should be possible to have only one big bitmap font and downscale to fit the needs and saving memory by not having 4 different size of the same font in the atlas.
- Fonts effects, the designed with whom I work wanted a text glow, and I had to have the same font twice in the atlas with one of the two as a blurred version but it takes an incredible amount of space.
- A timeline system for animating the GUI would be nice (think flash timeline), I know it is a huge feature, but would be very nice

Mathieu
EDIT:
- Better support of Perforce with the atlas maker, currently it ends in failure if I don't manually check out the texture files before updating the atlas because Unity only checks out the prefab file.