Twice as much fun :) Seriously? Twice as much work, twice as much milk. Supplementation is somewhat more common with twins, as not all mothers make enough milk for 2. Some can feed 2 simultaneously, some find it easier to feed 1 at a time. It rarely takes longer to feed 2: mothers of twins discover early on that feeding itself takes only a few minutes, and the rest of the time at breast is "entertainment".
Gets very busy. A mom can breastfeed twins, one at a time, or both at the same time. She'll be very busy, so should have a good helper, such as the dad.
Time consuming! Most breastfeeding mothers of twins find it best to set up a feeding schedule and gear the babies around the schedule. You can feed them both at once or alternate the feeds, starting each on the opposite breast.