One of the things I notice over and over again is that many applications clutter databases with historic data. It is actually no that hard for a programmer to make a maintenance plan as a part of his application.
Lets consider a real life situation. Most organizations have accountants and they generate quite some data year after year. Today were in 2008 and honestly, I still haven't figured out why the data of 2005 should be on the system. It is valuable to the organization and law demands to keep it but why keep it on a production system?