My favorite way to carry duct tape, is to wrap it around a Nalgene bottle. Then you can either use the bottle to carry a "kit" inside it, or to carry water; and your duct tape is always handy there on the outside of the bottle.
I got that idea from one of Cody Lundin's books.

Certainly, there may be times when you can't (or don't prefer to) take along a water bottle... so, use of the "card" or "self-rolled" methods will be perfect for that.
Otherwise, I like the bottle idea; because I always have the tape handy, and never have to worry if I packed the tape, or where I put it.