On a technical note, I have been working a lot with delegates in Objective C and they seem very powerful. They also work very well with the MVC pattern.
One of my main issues is working in the different view spaces. In my app I have to do a lot calculations for positioning different views pragmatically but due to the hierarchy of subviews you have to take extra caution to ensure you are doing the calculations relative to the same view.
Things are starting to pick up slightly and I will soon have a fully working prototype, once that happens I will upload a video and let everyone see what it is I am working on, but until then it's a secret ;)