What makes CGFloat different from a standard float, and why is the CG version needed when working with iOS UI?
One thing that bothers me about iOS development is there are a lot of prefixes and it is often unclear what purpose they serve. For example, it's not clear what the difference is between a string and an NSString (although NSString seems to come with some handy methods).
I can't think of any more examples at the moment but if you've worked at all with objective c I assume you know what I'm talking about and can help me to explain away some of this mystery.