The FTC report to congress on the CANSPAM legislation is available here. The report has been widely criticized for saying that the CANSPAM legislation was successful.
It says “since (the) enactment of CANSPAM, spam volume has begun to decline as has consumer frustration.” One of the notable aspects of CANSPAM was that the amount of spam skyrocketed after it was passed. Spamming was made legal as long as a legitimate optout address was provided and headers were not forged. Message Labs reports confirm that spam volume skyrocketed after CANSPAM and only since October have they returned to earlier levels. Causation has not been proven.
Consumer frustration has dropped because many ISPs and companies have added spam filters. The spam filter technology has advanced to the point that false positives and false negatives are minimized. Further several spammers have been taken out of the business by state attorney generals rather than FTC action. The FTC correctly reports that ISPs blocking of outbound port 25 except for through their own mail server has hampered the spammers abilities as well.