I absolutely agree that busting out the card or saying you won't talk without a lawyer is not going to make the problem go away. But if i were being detained and I was more than likely to go to jail, it is a lot easer to say in court "I handed the officer a written statement invoking my rights." than it is to challenge the word of the officer. It's definately not a get-out-of-jail-free card but it is definately something that people should be aware of, especially those that are not very secure in their knowlege of their rights. It's not for everyone, and not for all circumstances, but does have some value in our community.
Btw, those that asked about the canadian card, I found this, ironicly on a similear thread. Sorry for the double thread but here you go:
http://forum.grasscity.com/legalizat...ml#post1738663