The only flaw
with the endless rotating credit card balance
method, is that usually, they consider balance transfers
as a cash advance
. Cash advance fees are usually 2% of the transaction amount. So now you've gone from paying about 18% APR a year, to 2% compounded monthly, which is quite a bit higher.
Just paying in full every month and only using cards that have no annual fee means you're using other people's money to buy stuff--at least for the grace period of the card. Whose money are you using? All the dolts that don't pay off their balances in full.