1) When defining a new method in a header file, it would really be nice if I could click on the method name or something and say "Generate skeleton implementation in .m file"
2) If I create a class which inherits from some other class (which I guess is every class, eh), I'd love to be able to pick something from a menu like "Override Methods of Superclass"... I'm a newbie, so how in the heck am I supposed to know that my custom NSView subclass has a method called "(void)displayRectIgnoringOpacity:(NSRect)rect" that I can override?
There are probably hundreds of methods in the superclasses, for any real world class... you want it to override all of them? [[ long story short, it's impossible anyway, regardless of the fact that it's not what you really want ]]
In some cases Xcode has templates (e.g. NSView subclasses) which override the most likely handful of methods by default, which is a good start. Otherwise, the documentation will usually indicate what methods you may particular want to override.
Keep in mind, however, that the preferred pattern in Cocoa is not to subclass, but to delegate. Delegates are typically defined by categories or protocols, which provide a concise list of the methods you may choose to implement. Again, you can check the documentation and headers of the classes in question to find these.
And as a consequence of preferring this pattern, most Cocoa classes really aren't designed to be subclassed by anyone but the author, as they do all sorts of undefined things and have numerous undocumented methods and call paths, etc. So you'll want to avoid this where possible, where you're not explicitly told otherwise.
3) Like #2, if I declare that my class is going to implement a specific protocol, it would be nice to have some type of stub generation for everything that protocol defines.
Protocols may have optional methods, which makes this a bit ambiguous. You should file an enhancement request, though in this case I doubt it's considered a priority enhancement since it's pretty negligible extra work to copy-paste a line and replace a semicolon with a curly brace.
4) Maybe I don't get the shortcut keys or whatever, but when I call a method which takes many named arguments (say, NSImage's "drawInRect:drawingRect:fromRect:operation:fraction:" method), the auto-completion is annoying to me as you start working through each argument. For instance, when I type "[myImage drawInRect:]" and hit tab, it appropriately highlights the complete first argument (NSRect)rect, so I just type the name of my rect, and it's good. Problem is, I can't seem to find a way to then proceed to the next argument. If I hit tab, it just inserts a tab between the arguments. I then have to cursor over after "fromRect:", and then highlight the next argument's placeholder, then start typing... It's pretty annoying, but this one I'm sure must be a case of user ignorance.
In Xcode's preferences, go to the Key Bindings section, and you'll find the Code Sense keys right near the top under the Text Key Bindings tab.
5) In interface builder, why isn't the IB smart enough to auto-complete/suggest valid keypaths for me when I'm binding a component's value to some keypath (through the bindings inspector)? This would make things so much easier to just tell me what's available... The list always has one item in the dropdown, "self"... Properties of my object I'm binding it to are not in the list, and if I try to hit escape to do auto-completion, well, the window closes :-)
Again, this isn't necessarily trivial to do for certain reasons you don't want to care about, but it's well worth filing an enhancement request.
http://bugreport.apple.com/