Accepting a graduate offer of admission and then turning it down
Traditionally, the recommendation is that as soon as you are accepted you withdraw your applications to schools that are out of the running. Then as soon as you accept an offer you withdraw your remaining applications. If a school make a decision early and requires a decision before you hear from schools you may find more desirable, it is best to ask for an extension.

I go against the norm a little and believe that if a school/employer will not give you and extension and wishes to put you at a disadvantage that it is not unreasonable to reneg on your acceptance. As this is not the norm, it will burn bridges.