SpamCop and Unsubscribing does work.... sometimes.
Basically, there are two types of spam. The intentional spam, and the unintentional spam.
Intentional spam is anything XXX related, scams, schemes, etc... The person who sent the message *knows* they are spamming everyone. Most of the time you can identify these if they mention some Senate bill they are in compliance with (there is no such bill). The messages are usually sent by hijacking open relays, spamcop will do very little, and unsubscribing following the methods in the message will make matters worse
Then theres the unintentional spam. Most of the time it happens because a n00b Marketing Manager doesnt understand net-ettiquete and thinks that its ok to send people a message they didnt ask for, as long as you give them an option to opt-out. In these cases, unsubscribing will most likely get you off the list, and spamcop actually does its' job properly.
Bottom line is that unsubscribing and using spamcop will not work all the time, but it will work some of the time. It's sertainly better than doing nothing.