Like any other form of PvP, you either love dueling or you hate it. Dueling is a great way to learn how to maximize abilities and test combos and macros. There are very few established guidelines for how to appropriate ly duel. Borkovic of Caelestraz asked in the official forums if it is acceptable to heal in a duel. Fliara of Terenas stated that protocols vary depending on server and faction, and suggested that rules should be established beforehand.
The first response, by Mlcho of Kirin Tor who takes an "all's fair in love and Warcraft" approach, was met with considerable agreement throughout the thread:
Use everything in your power to produce a win. Who cares if you use a pot? Who cares if you bandage?
If they whine, it's because they weren't prepared.
When I duel, I do it to prepare for arena combat. As a Resto Shaman, my strategy tends to be to outlast my opponent, so healing is very important to me. I consider it to be using my class and spec to maximize my chances of success. I agree with Daneric of Moon Guard, "Saying no healing is like saying no stealth to rogues, no totems to shaman, no pets to hunters, et cetera..."
I do not use potions or any abilities that are not acceptable in the arenas. Sure I could drop a Fire Elemental Totem, but that doesn't do much to prepare me for PvP when it counts. It seems silly to me to blow an ability with a long cool down in duels, but I've seen it done. It makes me giggle.
What do you find acceptable and unacceptable in duels?