Originally Posted by aku
As a consultant, I've been told that my client will not pay me for hours spent flying, unless I am also doing work. I save up presentations, white papers, etc. to read on the plane

, but I still travel nights and weekends most of the time. Meanwhile, the client's employees pretty much always travel during business hours, to the point where it can be difficult to schedule around them. ("Sorry, I'm traveling all day Friday. Did I forget to update my Outlook?")
It depends on the deal you manage to negotiate with the client. I've seen both situations (client pays for travel time; client doesn't pay for travel time) and something in between (client pays 50% of normal rate for travel, or pays for travel time up to a certain cap per trip). Generally, I try to work on the flight anyway; so it does not make a big difference in billable time.