as soon as i got my very own personalized spam concerning their offer
to add a domain to ".CC" for me, we blackholed all of their mail and
web servers. since NANOG was discussing this a few days ago i thought
i'd better chime in.
But that's highly targetted email...not spam 
(round of applause from the RBL subscribers)
Thank you Paul,
...and since we just upgraded to sendmail-8.9.1, with rbl macros, this
means that I won't get my very own personalized copy of that spam.<grin>
BTW, we did enable rbl on our mail hubs and are using the DNS subscription.
Are there any issues I need to be aware of?