I've used them before, but they didn't make a cent off of me except maybe by getting surcharge from the seller. If you read the terms of the 0% loans and budget appropriately to pay off in the interest free period they are perfect when you want to avoid carrying a credit card balance or selling investments to make a large purchase.

However, I always recommend that people avoid these loans if they couldn't pay the loan off in less than a month anyways. Too many people get trapped by these. But the same could be said of credit cards and banking in general.