I've been playing around with my UI quite a bit recently, tried some elv/tuk, tried some minimalistic ones, even some class specific ones, but I can not seem to get use to them. I always find myself going back to default UI.
I was told to just PvP and do raids with them but after a few days, I still wasn't as use to it as I was default. I know where everything is in my head, but it takes just that split second longer to react them it would if I was using default.
I guess the question would be, how long does it normally take you to get use to a new UI. The longest I had one for was 4 days and I was never happier to see my old, default UI again. That said I do wan't a new UI, I love how some of them long and make information just that little easier to see, but I honestly can't see myself using one long enough to get use to it.