>I am occasionally annoyed by Not_found propagating to my
> top level function .. meaning the error could be anywhere
> at all in my program.

At that time the best is to run your program in bytecode with debug infos 
using ocamlrun -b so you'll get full backtrace informations. It would be 
better for such debug informations (not all the types but only the 
bytecode -> source positions) to be included by default, and always have 
backtrace turned on.

Nicolas Cannasse