quit for getting salary increased(090511)

Today, i saw some discussion on 6sq website about how to get your salary increase. and someone think it's a good way to bring a quitting letter for getting salary increased, i don't think so. the below case is what i have experienced.
in my previous company, I submitted the apply letter for quitting,but boss and general manager attempted to keep me. i persisted in leaving there although they committ to give me the same salary as my new company(plus the promotion as a tempentation),for i cann't lose the promise to the other company. Maybe i looked so foolish in that case but i never reget it when i recall this every time. On the contrary, i am very pride of this. After all, they admit my work value, that's what i want to get.

Though i am fully confident with my ability,but i don't dare to make the risk to quit my jod for the increase of salary in the current company.