I have started using the Three20 project for an iPhone/iPad application.
Did anyone face any issues during the submission process because of this? Also, how challenging it is to make the application iPad compatible - I am using Three20s navigation style, styled labels and photo controllers.
Thanks in advance for the help!
The current App Store status for Three20 is displayed at http://three20.info
It is currently App Store Safe.
I think you'd better use Apple's own UI elements, and just look at the source code of Three20 to learn their tricks whenever needed.
In my opinion Three20's code is kinda messy in structure, surely not as easy to get support as you do with Apple's standard UI elements, may break in future versions or future devices, etc...