The DNSBL spamtrap.trblspam.com appears to have gone offline as of April 2, 2013. It appears to have been created in early 2011 by somebody known as "Tom from TRBL," whom I observed participating in various email discussion lists. I've emailed Tom and will update this page if I receive any further details.
I recommend removing spamtrap.trblspam.com from any blocklist checking you're doing. Any time a list is shut down, there's a chance that they will end up putting in a wildcard DNS record, which ends up effectively "listing the world" and causing problems for any receiving sites who still have that DNSBL configured in their mail server configuration.
(Thanks to Martijn Grooten for the heads up.)