Also, hours billed can be a poor measure of how demanding a job actually is.

I had one horrible week a few years back where I was in the office from 9:00 am to 3:00 am or later every night, but billed less than 30.

Basically, I sat around all day, with nothing to do, and then got a call about 5-6 each evening, with an emergency assignment that needed to be handled that night.