Are you willing to elaborate on this? Recommending it over garbage collection on OS X would run contrary to their previous evangelism of GC and its concurrent scalability.
(I haven't done any Mac OS programming with GC, so I really don't know anything about it, but I've always heard people say the GC is not all that great. So my own uneducated guess is that while GC is messy and complicated, ARC is simple & doesn't have any runtime overhead (they say in the docs that retain/release is now much faster, as is autorelease using the new syntax).)