There's three laws of thermodynamics that need to be broken before perpetual motion has a chance.

1 - you can' t win
2 - you can't break even
3 - you can't get out of the game

By definition it'll never be an energy source, soon as you extract any energy it ceases to be perpetual (sheesh, why is perpetual so difficult to type??!)

If you reach cold fusion you've gone too far, and should turn back.
What?? You mean all that stuff I'm building in the attic won't work after all, damn you Lemur, and your bad news