Should I be required to act on this?

My friends all knew I have no desire to go the prom; when they bought their tickets, the impulsively decided to buy me one too. When they told me, I first thought they were joking; once it twigged they weren't, I politely said I honestly had no intention of attending, then recommended they get a refund for it.

The finance office rebuked this refund request, after which my friends told me I either had to attend the prom, taking full part in the shared group costs (limo, before-meal, etc) or pay them back for the cost. Should I feel obliged to do either, given that I didn't ask them to buy the ticket - they did that of their own accord?

Absolutely not. They knew you didn't want to go, and chose to get you a ticket anyway. You are in no way obligated to them for anything. And why should you get the ticket refunded? You didn't buy it. While their intentions were probably good, they are wrong. You owe them nothing.

You are not obligated to pay them anything - they bought a gift and cannot expect rapayment if you do not go. I think you should go however. It was very kind of them to think of you and if you don't go they will never do anything spontaneous and kind again. Its your call. but if you do chose to go you are also not obligated to take part in their other expensive activity.

Absolutely NOT! That is complete BS. People need to pay attention to what other people tell them. This is NOT your responsibility, and I would make it perfectly clear to them that you had no intention of going and you let them know that in the first place. You may lose some friends (temporarily) from your decision, but they will get over it.