If you are using SPS 2003 or MOSS 2007 with a SQL Server 2005 box that does not have SP2 installed, you may discover that your crawls never complete.  There is a bug in SQL 2005 that if you have a Reindex Maintenance Plan it clears some attributes of the SharePoint indexes when it reindexes which in turn breaks the search functionality of SharePoint.  Long story short, consider SP2 for SQL 2005 to be a system requirement of SharePoint.  More information available here:  http://support.microsoft.com/kb/930887