I've found that the "silent treatment" works when it is, as previously mentioned, for a predetermined time and when the sub is aware that it will come to an end (and when it will come to an end) -- for example, putting a sub in "time-out" (as was also mentioned) is a good way to not grace him/her with Your company and attention and yet not frighten the crap out of him/her by abruptly ceasing to speak or acting angry or otherwise cold.

What makes the "time-out" so effective for Myself and My Pet (or so I've found) is that I make her sit in a corner, turn off her wheelchair so she can't move, and face the wall without speaking or interacting with Me. I then also sit silently on the couch or somewhere nearby -- close enough that she is aware of My presence and of the fact that I'm doing nothing but watching her, but far enough away or behind her that she can't communicate with Me, even with her eyes. She says this is the "worst feeling" because she feels that it is a punishment for Me as well as for her, since I do nothing and basically stare at the wall with her. Were I to, for example, play Xbox or do some other activity I think it would be less effective than the dead silence that falls over the house when she's in "time-out".