If you take into account of most Frequently Asked Questions in any SQL community forums, you will get to see problems against database maintenance plans by the users. Personally I don't like them to use (by default) and professionally always depend (suggest) upon my own scripts to manage the backup & database re-org processes. So coming to the common problem faced by the users is, say X has created a Maintenance Plan to do a nightly full backup and set the backup set to expire after 2 days. Weeks...(
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Read the complete post at http://sqlserver-qa.net/blogs/tools/archive/2007/09/07/sql-server-2005-maintenance-plan-not-deleting-old-backups.aspx