More than seven years after I initially started the backports.org project together with Team(ix), my employer at that time, it finally happened: backports.org became official last weekend, and moved to backports.debian.org! Alexander Wirt wrote a blog entry including some technical details, and there is also an official announcement on the debian-announce mailinglist. The most important point from a users perspective is to update your sources.list entry to:
deb http://backports.debian.org/debian-backports/ lenny-backports main contrib non-free