Too bad javascript doesn't have tail call optimization...

+1 for solution using tail recursion

This is awesome.

I would say be careful about using getOwnPropertyNames. If someone creates a non-enumerable property on an object, chances are that they're explicitly looking to hide that property from enumerations, (i.e. most of the methods attached to Object.prototype). When creating a method that's supposed to return an object's keys and values, I've always found it more effective to honour the integrity of the object being passed in by only looking at enumerable properties. Otherwise the author of the object wouldn't have gone out of their way to explicit make that property non-enumerable. Just a thought!