I agree with quite A few points raised here...
1. If you crash its your fault not the marshalls so get over it.
2. Yes the burns do hurt a lot!
3. In my experience, generally the better drivers are the first to complain and the last to react when marshalling (not all though)
Now I'm not the best Marshall, but I do my best, heck I'll sprint to a car over the other side of the track of I need to, and I generally come back from marshalling a bit "tired" from running so much!
And I'm done
