From Seo Wiki - Search Engine Optimization and Programming Languages
SURBLs (no longer an acronym) are lists of Uniform Resource Identifier (URI) hosts, typically web site domains, that have been observed in unsolicited messages. SURBLs can be used to search incoming e-mail message bodies for similar sites to help evaluate whether the messages are unsolicited. For example, if http://www.buypillswithoutprescription.com is blacklisted, then e-mail messages with a message body containing this URI may be classified as unsolicited. SURBLs differ from prior DNSBLs, which commonly list mail sending IP addresses. SURBLs are a specific instance of the general URIBL list type. URIBL.com is a different, unrelated URIBL-type list.
SURBL.org claims overall false positive rates between 0.001% to 0.05% . However, one list in particular, ob.surbl.org, uses not spam reports, but content analysis rules, combined with the age of the domain. Critics believe this unjustly punishes legitimate startups and SMEs, many of whom will be unaware of the problem and have their email capabilities restricted with no knowledge of how to solve the problem, or even that it is occurring. 
Response to Criticism
The above criticism appears to claim an internal knowledge of a blacklisting process which would probably not be visible to the critic. For example, the ob.surbl.org list does make indirect use of user reports, but with extensive filtering. The blacklisted domain was apparently quickly removed from the blacklist as result of the critic following the clearly and prominently published removal instructions. Therefore it would appear that SURBL makes a good effort to remove legitimate sites.
The most likely reason for the blacklisting is that messages from the Yahoo Groups referenced were gatewayed to email and reported as spam by some of Outblaze's 40+ million mailbox users.
- DNSBL, a spam prevention method in which e-mail messages are accepted or rejected depending on the IP address of the mail server from which the message is received