I'd say about 5000 would be good while still remaining at least somewhat reasonable to do (though rather tiring, sorry craig). My reasoning behind this is as follows: 3 years of fairly heavy usage (15 opens/closes a day) would come out to just over 15000, and the way craig is doing it should be equivalent to at least 3 normal open/closes. And 2 years of heavy usage like that should translate to at least 5 years of average usage (5 open/closes a day?), which seems acceptable. More would of course be better, but I'd imagine it would take a while and 5000 should be plenty. Though if we're really lucky, it'll be able to outlive the GBA SP's hinge, which is capable of withstanding constant and severe abuse of the worst kind (AKA me when I was 10).
EDIT: had 10000 instead of 15000, oops.