Okay, "perpetual motion machine" might have been hyperbolic -- the comparison I had in mind was to what we might call a "weak" perpetual motion machine, which doesn't generate energy but is exactly frictionless, so it twirls forever without energy input.
So, don't get me wrong, it's a nice hack, but it's hardly perpetual or earth-shattering. One similar trick I know of is to have several credit cards, and use them to keep transferring the balance between them before interest accumulates; but this is less efficient, since the "free balance transfer" special offers occur relatively rarely.
Interesting! Didn't know about that variant.
Do it for long enough and inflation will eventually reduce the debt to a negligible amount. In twenty years, at three percent rate of inflation, your debt will only be worth 54% of what it initially was!
Thus spake Eliezer:
It seems that many here might have outlandish ideas for ways of improving our lives. For instance, a recent post advocated installing really bright lights as a way to boost alertness and productivity. We should not adopt such hacks into our dogma until we're pretty sure they work; however, one way of knowing whether a crazy idea works is to try implementing it, and you may have more ideas than you're planning to implement.
So: please post all such lifehack ideas! Even if you haven't tried them, even if they seem unlikely to work. Post them separately, unless some other way would be more appropriate. If you've tried some idea and it hasn't worked, it would be useful to post that too.