Hmm, what problems are you having as a warlock ? The only minor problem I came across was the pet bar not displaying properly but I recently created a macro that helped resolve that and posted it on the site here for people to use in the interim.
Please bear in mind that there is only 1 developer for this addon and he is also trying to get the next improved version out of the door too. He is only 1 man and can only do so much with his spare time once work and family have had their share of his life. Whilst it may look like he has a group working with him we simply help out where we can but in the end it is only Scott that can make the final changes to the project itself.
So in answer to your question: I am using nUI because it is as close to a UI that I would have envisioned writing myself one day. But, whether I would have had the commitment to keep it going as long as Scott has is another matter. Bear that in mind
The project I am sure like many others started out as a personal UI design that gradually exploded onto the scene as more and more people wanted to use it. The more people that use it increases the more chance that something is spotted that wasn't planned for. This happens in programming unfortunately. But as has been said. Any serious problems that are reasonably simple to fix has been fixed within a week of it being reported. Can you say the same for every other addon you have that is as big with just the one developer on the case ?