The BSB is a database of IP addresses that have sent "comment spam".
You can use it for example to mark submitted comments and trackbacks for review.
To add BSB lookups to your weblog software, make it lookup
[reversed IP].bsb.empty.us. For example to lookup if
10.1.2.3 is in the database do a DNS request for
3.2.1.10.bsb.empty.us. Entries in the database will
return an A record of 127.0.0.2.
The domain lookups are in the same domain, so to lookup example.com,
lookup example.com.bsb.empty.us. Or if the comment you
get includes the url http://poker.example.com/poker.html
then check for the existence of
poker.example.com.bsb.empty.us.
If your weblog software blocks/discards the comment rather than just sending it to moderation or some such, please tell the user that on the weblog site rather than redirecting them directly to BSB.