bl.spamcannibal.org is notorious for a higher error rate (false positives). It'd be crazy if a popular mail service provider like Yahoo categorized incoming mail based on results from Spam Cannibal. If I added them to my MTA, I'd rank them fairly slow to diminish the effect of their false positives. See here: http://dnsbl.inps.de/analyse.cgi?type=monthly&lang=en

And see here how to add them to your checks (and rank them accordingly) if you're using Postfix: http://www.postfix.org/POSTSCREEN_README.html