Not me, the leaves are too big and end up shading everything else out.

I also don't think it would work. I almost question if they need even more room than 1 square because my cauliflower and broccoli shade everything around them.

No. Actually, I've never done well at 1/sqft. I checkerboard mine.

Definitely not. They almost need 1.5-2 squares per plant...

I think ribbit's idea of checkerboarding the broccoli will show great results--if you have the space to do so. The other squares can grow things like radish and/or carrots. They are quicker to mature so in theory, they shouldn't get shaded by the broccoli's leaves...

I've found a compact variety that I'm trying this fall; Waltham 29. There may be other compact/dwarf varieties out there, but this is what a local seed supplier had on hand. http://www.sustainableseedco.com/waltham-29.html

Here is a link that might be useful: Gardening With Care

It looks like I will be the only one who answered yes to your question. My brocolli did great this year and I had two per sf. I just had to watch them closely and trim any leaves that infringed on it's neighbor.

I had never tried them before, but I have been really happy with the results. In fact below is my daughter holding one:)