The Ethics of Bank Bonuses

Last year I made about $1000 from bank bonuses. It looks like I will probably make about that much from them again this year. This is easy money since banks pay you just for opening a bank account. Their hopes are that once you sign up you will remain a customer.

Since I usually open these bank accounts just for the bonuses and then close them as soon as allowed under the terms of the bonus some feel that I am being unethical. I feel that since I am meeting the terms the bank made that there is nothing wrong with what I am doing. Sometimes I open an account for the bonus but end up keeping the account because I like it. ING Direct is an example of that. I opened the account for the $25 bonus and have kept it for years. Also, I have referred over 100 customers to ING Direct. I suppose some of those customers were also only opening the account for the bonus but I do not feel responsible for their motives. I feel like I have earned my bonus from ING Direct.

What do you think? Is opening a bank account just for the bonus unethical or just taking an opportunity the bank is offering?