Regarding ASICMINER, 10% of hashing power is a very high share for me. If we end up with few players that constitute 51% of hashing power, that would be a threat to stability of the system, thus reducing it's trustworthiness.
I understand that having 10% rather than 1% is more profitable, but it may ultimately hurt the whole bitcoin ecosystem.
Over time, this will be a minor problem as technology becomes more available and shared across a larger user base. In the short term, it can even be beneficial to the credibility that there are a few major players that increase the total hashrate by such an amount, thus making the network more resiliant to a rouge entity wishing to attack. Right now, we know there exists enough hashing power to take over Bitcoin; with AM, Avalon, BFL, 100TH, and others adding network power, that becomes less likely.
.b