This is an interesting discussion that seems to stem from the counsel to always follow one's opponent or not to move unless one's opponent moves, and then to move first. I have always thought of these not so much as a literal requirements, but rather injunctions to begin any encounter with listening energy (ting jin) and then to act appropriately.
I also think it is important to realize that the latter half of the principle of not moving is that when the T'ai Chi player moves, he or she is supposed to be so "reactive" that he or she must move first, rather than second. Similar to what Michael says in his post, I do not think that the emphasis is so much on favoring yin actions over yang actions as on engaging in the proper interplay of the two.
In my opinion, one of the great differences between T'ai Chi and Karate (for example) is that T'ai Chi presumes that through sensitivity any energy can fairly easily be transformed (hua) into another energy that is either harmless to the defender or that will lead the attacher into vulnerability if the attack is pursued home. The important thing then is to hear (ting) the attack coming, understand it (dong), and transform (hua) it into something useful. Every encounter is a product of the actions of both people, and so no result can be presumed or planned in advance.
Karate tends to treat the opponent as a target to be struck or a threat to be avoided, so that victory comes from superior strength, speed, and technique to get to the decisive point of contact quicker and with more power. When you see an opening to launch your attack, your opponent's actions are hopefully irrelevant, because they will be too little too late. The quality of the opponent's energy is really not taken into account.
If confronting a master, it is probably foolhardy to initiate any action that might expose weaknesses; but if confronting a mere mortal, I see nothing wrong with probing and testing for a response. You begin by feeding only small amounts of energy into the encounter, but if your opponent's response is not appropriate, you continue to up the ante.
After all, if what you "hear" after the beginning of an encounter is a yin response or a passive disposition, I think one must "follow" your opponent by "initiating" a yang response in order to comply with T'ai Chi principles. Initiating, however, does not mean that one pursues an attack home, because that would mean not "listening" to the opponent's reaction to your initial action. If your opponent cannot demonstrate understanding of your actions (dong jin) or of transforming energy (hua jin), why worry about exposing yourself?
I agree that thinking about getting in the first punch is not really consistent with the T'ai Chi approach of following one's opponent, but I think that feigning a punch or even initiating one is okay as long as you do not abandoning a "listening" attitude. In effect, you initiate a meaningless attack that triggers or forces your opponent to "move," and then you react appropriately.
You are simply asking your opponent a question and listening (ting) to see if they know how to respond. If your "question" meets no response, you press the attack home. If you hear (ting) an answer, but nothing more, you abandon your initial "attack" and probe somewhere else. If your opponent not only answers your question, but asks a question of his or her own, you abandon your attack and answer your opponent's question by "transforming" into a new probe/attack/question of your own.
Another way of saying all of this is that I think that the mere fact someone stands in front of you and by word or deed declares him or herself your opponent gives you enough yang energy to work with or is enough "movement" that you must now "move" first. I think the trick is in "moving" appropriately.