I've currently got around a $10k balance across two credit cards. I currently pay no interest because I'm in the promo period. As long as I make the minimum payments, I'm getting an interest free loan for another year or so. I'm currently on track to (easily) pay these off before the promo period ends. I actually have the money to just buy the stuff with cash, but I'm using the 0% cards to float the costs for awhile and maximize cash flow.
Though I'm not planning to go this route, I was thinking: In the event I didn't quite pay down the balance on one card by the end of the promo period, couldn't I just do a zero-fee balance transfer to another "0% for 18 months" card? Assuming these offers don't go away (they've existed for many years now), what's to keep me from just carrying a balance forever and never paying a dime of interest to any bank?
In the meantime, I'd get to buy new stuff any time I wanted with a same-as-cash payoff arrangement and use my continued cash flow to maximize profitable investments in the meantime. It would be the long-term version of what I'm doing now, I guess, but it would involve perpetually transferring balances from one 0% card to another for... I don't know. The rest of my life?