Actually, the island of Montreal is more or less divided language wise along the East-West lines from downtown. The further west you are the more likely you are to hear English spoken and the further east you go the more French the neighborhood. On the whole, I would say that 75% of the pop understand both languages (and better than they give themselves credit for, or will acknowledge) at at least a conversation level while 50% can (if they wanted to) actually communicate in the other language. Your location on the island would influence that as well. Downtown is relatively bilingual, it is just a question of how interested they are to speak the other language. Don`t ask, 'cause I really could get into pages and pages as to why quebecers can be so........."reluctant" to speak their non-native tongue.
Now Back to RR's comment.....Just because I can speak it does not mean that I have much opportunity to actually write in the language. Read and speak I can do, french spelling and grammer.......not so much.