Hi, I'll be transferring to mac from another university. I'm wondering if there's a general 'must knows' page about courses at mcmaster? You know, just a page where I can enter the course name or number and see the discussions and opinions people have had in the recent past.

I've done a lot of searching in facebook and there's all kind of groups but nothing relative to the above.

You mean like these forums?

Ya these forums are your best bet at anything like that. Just go to 'Course Reviews' at the top of the page and most have lengthy discussions about how the course is set up, markoing schemes, thoughts on the prof, etc. Just pay attention to the date people submitted their review, as I've found the course reviews on this website now are getting fairly dated.
In terms of using Facebook, generally someone enrolled in the course (or you can) will make a page for that specific class for that specific term and others who are taking the same class will join it and discuss projects, test, etc. during the term. I suppose you could find older class groups on Facebook and message some of the members who are still in the group for their thoughts.