I'm a hunter, and I've found that if I'm riding around and get into combat with something, then dismount... my petbar does not show up. The only way I've been able to get it back is to do a full /console reloadui... that's somewhat annoying
Otherwise, nUI looks great. I would like to be able to save state somehow... I also use Cartographer and it's scale settings seems to get ignored when I open it up.