I should clarify that you and the client should talk about this beforehand and it really matters what you're hired to do. If you're building someone an e-commer

I should clarify that you and the client should talk about this beforehand and it really matters what you're hired to do. If you're building someone an e-commerce site and you decide to work on your iPhone puzzle game at home, its doubtful there'll be problems. But if someone has hired you to come up with ideas and program them, then you've really sold your idea making process as well as your coding skills, and it will be harder for you to claim ideas as yours.