I really enjoy the perspective that "now" is often a useful abstraction for certain types of processes. The fact that it turns out that "now" is one hellishly leaky abstraction. My perspective coming from biology is that for many systems the only meaningful type of "clock" is a logical clock. The important thing is not "when," when is used as a proxy for an assumed state of a remote part of the system (even if remote is only 10cm away), logical clocks are the only source that can guarantee that the state of the system is what you expect it to be so that it will perform as expected. Thanks to the many hardware guys who have spent years working out the underlying logic for this we mostly ignore it for things like processors. Now we just need to solve it for arbitrarily large finite delays! This also reminds me of a very funny (or depressing) read on systems engineering by James Mickens [1].
1. http://research.microsoft.com/en-us/people/mickens/thenightw...