I may be way off base, but as an Objective-C programmer for going on 3 years now, I just can't imagine why anyone would ever want to do this to the language. I had a longer rebuttal here, but I started to get mean - so I best just leave it alone. :P
I'm not sure Objective-C is going to benefit a whole lot from generics. The id "type" handles things pretty well so I don't see a whole lot of benefit here for the hassle of implementing it.
When they added Generics to Java I thought "this might be a good thing" then I started to use it and watch others use it and I think "wow they really screwed the pooch on this". The error messages are a total failure.
