I'm doing my masters here this year and from my experience (the people I've met), final marks are not that important at all. Obviously most people who are here will have a decent undergraduate degree but there a few who didn't even complete their undergraduate degree and still got in!
Everyone I have met so far has a very interesting background though, dual nationalities, lived in various different countries as well as having unusual interests or hobbies.
Obviously this is specific to postgraduates but I'd say it is very important that you can show that you like to get involved and have done things that are just a little bit different..