http://www.spamhaus.org/zen/
steve linford of spamhaus has recommended that people switch now: "> Is there any reason not to change? None, I advise everyone to change now. The SBL-XBL zone will continue to exist for some time but will not of course contain the new PBL DNSBL and will not contain other future DNSBLs we may release. ZEN is designed to be safely hard-coded into spam filter appliances and commercial filters." i presume this will have effects on the SBL- & XBL- related rules here.
