The question was raised at the cataloguing meeting this morning as to when authority records for series titles was discontinued by Library of Congress. Time flies.... it was June 1st,2006. Here is a link to LC's policy about what they do with series titles: http://www.loc.gov/catdir/cpso/series.html . According to this document, their decisions was "not to create/update series authority records and not to provide controlled series access points in its bibliographic records for resources in series."
This document also says that there is more information about series titles and the 490 tag in the Cataloger's Desktop. Our subscription has been renewed so we should have access again if you want to read more about it.