Not sure how common this scenario is, but something to be aware of if you are using DB snapshots (SQL 2005 & SQL 2008 feature) and a 3rd-party backup tool that acts on the database files.
SQL Server 2005 introduced snapshot databases and modified DBCC to create secondary snapshot streams for online DBCC operations. The online DBCC creates a secondary stream of the database files that is SPARSE. CSS has found that if a 3rd party backups and utilities or NT Backup is used against the database files the SPARSE setting may get incorrectly, propagated to the parent stream. In the case of DBCC this is the original database files(s).