I'm not a lawyer (and await Sparteye's more detailed elucidation on this), but having been involved in the negotiation of a couple of international treaties, I can tell you that the lawyers at the US Department of State feel that "shall" is strong stuff indeed. The first international agreement I've had anything to do with was full of that word, and it took FOREVER to get even the little pieces done, because "shall" was seen as so very strong and binding. Working on a less lofty agreement (I believe, in fact, we had to call it an "arrangement," as agreement meant a greater commitment than was intended), we had to use "should," because it was not going to be signed at the executive (i.e. Presidential) level.
Ever since I've had a very strong feeling that "shall" carries the most water among the wills, shoulds, woulds and coulds.
p.s. Sparteye - I imagine you know this, but I winced when the spellwrecker rendered your name as Spasm. It thinks mine is Hyman (yes, spelled with an "a" - which is not a word I know).
Hyla
