As Necrophobe's post show's you, most the discs have way too far of a reuse time to be effective in group, although you could probably use them all one time if you had an endless supply of Endurance. Endurance does not have any way of being replenished outside of just don't do nothing for a while. It will eventually build up, but the time to allow for this is just way too long of a downtime to actually let this stop the group from grinding.
Another thing to note, and I'm gonna use Defensive as an example.
Quote:
Lvl 55
Defensive Dur 3 min Reuse 15 Reuse (lvl 60+) 10
The warrior takes less melee damage, but also deals less. This discipline lasts for 3 minutes, and has a base reuse time of 15 minutes. The reuse time for this discipline will decrease as the warrior gains additional levels.
At level 70, it lasts for 3 minutes and has a 7 minute refresh. The other's are pretty similar, if it says 60 minutes, at level 70, it's about 55 minutes give or take a minute or two at most. Considering that a group in an Ldon or DoN mission lasts about 1 hour, the chance of using anything more then once is pretty slim, outside of your berate line. You could probably use defensive twice though, endurance will not hold out if you push it soon as it refresh's, you will find yourself OOE (Out of Endurance) Pretty fast.
Use the discs for what the rest of us use them for, on Named mobs, Raid mobs, and even epic mob's. Save them for when you really need them (Example: Cleric hollar's OOM and mob isn't dead, hit that Furious Disc before you die, and reposte as much as you can, who knows, might be able to win if DPS In group is good enough).