What a coincidence... I just picked up PCP1.com, which was dropped today. I think the value of such domains depend on many factors. A very important factor, in my opinion, is the relevance of the three letters. For intance, PCP is a very used acronym for primary care physician. That must be taken into account. In this case PCP1 is also the name of a mitochondrial enzyme. In other words, in addition to the fact that the name is short, its relevance increases when it is meaningful.