I also love Montréal but what kevincrumbs describes is just one of the many super irritating things about its public transit system. The UI of the ticket machines is from the middle ages (but probably written entirely in French) and to this day, it is not possible to buy a weekly pass starting any other day than a Monday, or a monthly pass starting on any day but the 1st of a month. God forbid somebody arrive in the city on a Wednesday the 5th....
Probably to hide their embarassing ineptitude, the STM transit authority has recently made their stm.info website unreachable from outside North America - which does of course not stop the Bureau de Tourisme from linking to it. European travellers love it!
And as for the REM, well... câlisse!