It depends how you frame the time in question. Is this 4 hours and 30 minutes of heads down, in the zone, productive work? Or is it a mixture of emails, conference calls, and coding?

In my experience managing and being part of various teams and projects for over a decade, I have found that a senior level developer that gets 4 hours of productive work done each day (over a week average, often not in one spurt, depending on the individual) is worth his/her weight in gold.

I always try to encourage 40 hours a week of being online, available, dealing with meetings and whiteboard sessions, but 1/2 of that devoted to heads down work like coding or designing. Often many people that are extremely valuable end up getting less than 20 hours a week of real focused work done in my experience.