I'm 20% too. I was really upset at first when I saw so many acceptances/rejections a few weeks ago... Now I feel a bit of solidarity with the other 20-percenters.
I'm assuming most of the 20% left are apps where the two readers had split decisions. For instance, I'm sure my work experience and grades are probably fine but my "quant" skills don't look as sharp (though they are. no really. they are. I can graph you something if you'd live). I guess it's better to be re-considered than outright rejected? Otherwise, if you speak 7 languages, went to an ivy league school and you're a lawyer.... I'm totally screwed.
It's terrible that they are taking so long on our applications. I've alienated a lot of my friend recently, lashing out at people. Not sleeping well. Drinking too much. I got sick last week with a cold... And don't even get me started with my focus at work...