You'd need to check the terms & conditions of the specific offer to be sure. In many cases the 0% applies to the balance transferred and any subsequent transactions while there is any of the transferred balance outstanding incur immediate interest charges at the normal rate. Some offers may be different but I believe that this applies to many of these. So basically the 0% balance transfer is only of use if you are not going to use the card at all until the balance is cleared. Caveat emptor.