I like that phrase.
I work in an association with hundreds of active members and a vibrant, responsible staff. We have about 50 projects going on at any one time. To keep all these balls in the air, we matrix manage. On some projects, I'm the leader, and on others I complete tasks for other leaders.
When delegating responsibility, there's no better response I like to hear than "Will do!"
"Will do" shows you are a responsible, can-do person that is an important part of the team. You are the kind of person others want to be around.