I think what is more relavent to me as a developer is how it will actually be implemented. I'm not too concerned about the performance (I'm sure Apple can do a decent job), it just seems to me that it could easily end up being only slightly easier to use garbage collection.

From a personal perspective, I have a pretty good grip on memory management now, and when I do I cock it up, it's generally due to an error in my design, rather than the lack of a garbage collector. I find that the memory management tends to correct me when I'm wrong!