I hear pros and cons to both sides of the argument.
On one side, you don't want to have your chest cavity slam into that big ole steering wheel while your face goes thru the laminated glass..
..on the other side, to you really want to be strapped to the wreckage?
I had a seatbelt lock me in once.. I went to the 7-11 to get smokes and when I tried to get out, the seatbelt wouldn't disengage.
I tried for close to 30 minutes to get it loose.. finally I said to heck with it and pulled out my pocket knife and cut the belt.
I think the best way to avoid injury is to drive defensevly.. keep your eyes moving.. leave yourself and out.. make sure they see you.. aim high in steering.. stuff like that.
I wear my seatbelt in the later model vehicles just because I don't want to pay a ticket.