I found this great post from Marketing Pilgrim. I have always told people that from a marketing perspective, unless you are selling to teens, people who frequent clubs or late night parties, people in the music industry, or people who work in adult industries, MySpace is a waste of time.
I also think that there is potential to actually damage your brand if you have a big presence on MySpace and don't want to be associated with the elements of the MySpace brand. I think Cartier is making a big mistake. I mean, there are so many other options out there... why choose MySpace?