People often ask me what to do with their estate plans when they move to another state. Here's the answer: if you think you're going to be in that new state for a while, it makes sense to update your estate plan to reflect that state's laws.
It's not that your estate plan will be invalid in another state. With the exception of gay marriage (in some states), contracts signed in one state are valid in another. But it can create inconvenience for your heirs if they have to administer an estate under, say, California law, if a parent died while residing in Georgia -- especially if the kids live in Georgia too.
Also, powers of attorney, which are important legal documents granting another person the right to act on your behalf with respect to property and health care, are created by state law, and your rights, especially with respect to health care decisions, vary from state to state. For that reason, and additionally because banks and doctors like working with forms that they know, it's a good idea to at least create new powers of attorney if you move to a new state.
For a comprehensive guide to estate planning essentials, see Plan Your Estate, by Denis Clifford (Nolo).