it's always seemed excessive and inefficient to me, but as said most anything will work if you stick with it...
i'd get a pull-up bar, a kettlebell, and do pull-ups/chins; pushups; kettlebell swings and spend half the time doing it...
or You Are Your Own Gym has a great list of body weight workouts that can be done at home, scales from easy to crazy:
http://www.amazon.com/You-Are-Your-O.../dp/0345528581
and dialing in your diet will have a greater effect than all the 'core work'...