The beta 1&2 font was Helvetica Neue Light, not UltraLight. UltraLight is so fine you can barely see it at normal size (I was going to use it in an app I'm working on, but ended up going with Light since it's much better). Now they're just using Helvetica Neue Regular.
I preferred Light, myself. I really hope they change it back for beta 4.
Regardless there are already numerous discussions on this though...