It is nice in some cases, but for example, string manipulation is pretty hard to parse compared to python because frequent operations are huge sentences. Pulling out json data that is presented as NSArray's and NSDictionaries was especially painful. That large amount of text makes it slower to parse and and thus your less productive. As PG said, the consistent factor in bugs seems to be lines of code. The more verbose and boilerplat-ish a language is, the more likely your going to have slip ups that cause bugs for similar functionality.
Ex:
[NSString stringWithFormat:@"%d items", itemCount] vs.
"%d items" % itemCount
or
json[@"keyA"][@"keyB"][0];
vs.
[[[json objectForKey:@"keyA"] objectForKey:@"keyB"] objectAtIndex:0];
I actually like the selector syntax. I have type ahead and don't have to constantly look at code to figure out what parameter number something is.