The silent treatment would be an awful punishment tool in my relationship. I found this out the hard way. The one time I did something that required an actual punishment, I wanted to continue to discuss it (we were chatting online), though our relationship is not online, but RL. Sir was pretty pissed (to put it lightly) and said he'd get back with me "shortly".
I didn't move from my computer for hours just waiting for him to return. I was literally distraught. Apparently, I had/have abandonment issues with him; this surprised us both as I'd never experienced this sort of issue in previous relationships; than again, my other relationships were non D/s.
If I was this upset and only a few hours had passed, I'd hate to think how I'd react after a few days. Thankfully, Sir will not use the silent treatment as punishment and I try my darnedest not to give him reason to punish me.
By the way, that short bit of silent treatment wasn't even meant to be punishment; he just had a few other things to do. D'oh