I was there at the time but to be honest I don’t remember exactly. I know that we used to use Photoshop for mock ups. I think one of the other developers found Balsamiq when they were looking for something that would be less work and we found the side benefit that the doodle looking mode prevented confusion.

Whether we realize that immediately or only after we stopped having misunderstandings I’m not sure.

But once it was realized I don’t think it took very long at all for it to become a rule. It made life so much easier for us developers.