To avoid this, when working with my laptop on an airplane in economy, I often will lay the screen flat on my lap, and have the keyboard against my stomach. It's a little harder to type, but you don't have to worry about the dude in front of you smashing your screen.

Of course, I don't like to work on the plane, don't do it very often and try and limit the amount of time my laptop is out. If I had a lot of work to do, it would be very inconvienent to have to work like that for hours at a time.