A comment in the posting of part 2 of this series mentions how poorly adding Web sites has been done. That is no reason not to do it right. See the poster from the OLAC conference Building a Virtual Library Collection through Freely-Accessible Web Sites : Select Web Sites Database at the University of Vermont, presented by Wichada SuKantarat and Kor Kiley on how to do it right.
Broken links are mentioned in the comment. They do need upkeep, but that need not be a large burden. Tools like PURL provide a way to distribute upkeep and a method of checking. MarcXGen is tool to use when doing the checking locally. Selecting Web material of lasting value will also lessen broken links. The links I have to the NASA History Office publications have had no problems, I can recall, for several years. The GPO is creating PURLs for the on-line materials they catalog. Those should have stable links and get fixed when any number of libraries notice a broken link.