I used to use 20 but now I keep it to 18, 16, 15 or 12.
I don't think I ever got rejected for using 20, but it always seemed like I was pushing my luck.
Plus, with different "shape" recip tables, (3x6, 3x5, 4x4), it encourages me to use different layouts and helps with the freshness of the freesite.
I think.
