You know, now that I think about it I suppose the Post It's aren't terribly necessary. They do prevent the tiny steel wool fibers from getting all over the fretboard, but a can of compressed air should take care of that problem. It's just a different method of accomplishing the same thing, really.
If it's a question of masking tape vs. Post It's though, the Post It's definitely leave less residue ... much, much less. And if you're going to be cleaning the board anyway, do what you want.