I'm with the OP on this one—wireframing on the computer is unreasonably slow. It's four to five times faster to draw something out on paper.
Seriously, try it. Come up with a design in your head. Try drawing it on paper. Then put the paper away, and try drawing it in Mockingbird or HotGloo. It will take significantly longer. And worse, it feels like wasted time, because you know you could do it much faster.