Curious regarding those who opened 529s in other states. Presumably tax deductible? How does that all work? E.g. where did you go to open the accounts and do you have to end up filing taxes for the particular state you opened the account in, etc?
If you live in California, you are
not going to get a state (nor federal) tax deduction, no matter what state you open the 529 with.
So no, you don't have to file taxes in any other state.
People, like me, open up a 529 in other states because we like the investment options better: lower fees, better investment choices, etc. Read the article I linked earlier about best 529 plans.
If you live in a state like California which has no state tax deduction, there is no advantage to open a plan with your own state, so you are free to the choose the best one nation-wide (or not open one at all). If you are not getting a state tax deduction, the case for opening a 529 is limited, IMO.