Is it possible to use interest earned on a position to make real money?

Has anyone ever used interest earned on a position to make significant money? For example, entering a long term, relatively safe trade (for example, buying EUR/USD once it bottoms out, and holding it for 6 months) to benefit substantially from the interest rate?

Or is this a waste of time/stress/money?

Called "carry trades" and yes, it's very common. But it's not nearly as straight-forward as you might think.

yeah.. if the prices move against you, the relative little interest u gain will not help!