This guide will show how to remove the motion blur effect independent of which shader settings (High/Very high) you have assigned:
1.Go to Library
2.Right click on Left 4 Dead 2
3.Select "Properties"
4.Select "SET LAUNCH OPTIONS..."
5.Paste this command: +mat_motion_blur_percent_of_screen_max 0

DONE!!! That's it! (also works in Portal 2 and Left 4 Dead)
Less fps drops, no terrible blur effect or motion sickness!

Note: You have to paste the command directly into the launch options, it won't work if you type it in the ingame console!

Want to enable it? Click here: http://steamproxy.net/sharedfiles/filedetails/?id=1103642030