If the address is in the Paypal transaction, I'd just ship it. We used to worry about it, but it happened so many times over the years and we've had no problems.
If it's a totally different address--not in the PP transaction, then it's a case by case basis. Sometimes it's a gift, or being sent to a kid at college... most of the time it's not a big deal.
If they buyer updates their address in PP, it won't be reflected on your transaction, so you'd need to refund & re-invoice them through Paypal if you wanted to see that address in the PP transaction.
