I realize I am way late for this party, but I would like to make a specific theoretical point about synchronous vs. asynchronous communication. It turns out that, given some components or modules or threads or what-have-you communicating via sending messages to one another, synchronous communication is actually more general than asynchronous in the following technical sense. Once can always use synchronous communication to implement asynchronous communication by throwing another module in the middle to act as a mailbox. On the other hand, given only asynchronous communication, it is impossible to implement synchronous communication. Thus, I dearly hope, unlike nazgulnarsil3, that I never see the day where we forget that synchronous communication is strictly more powerful than asynchronous. Moreover, this is not analogous to the wood/nonwood situation where they are entirely different--in fact, in the synchronous/asynchronous situation, one entirely subsumes the other.

This says nothing about that fact that it requires more computing power to encode asynchrony as synchrony (although only linearly more in the number of communication channels). Moreover, it certainly says nothing about central vs. distributed models, which is an orthogonal issue to synchronous vs. asynchronous communication.