Back model up (and also I often take copies of its data and log files). Otherwise recovering from a corrupt model is an absolute pain.
It doesn't need to be backed up regularly if you never change it, just have a valid backup as of the last time a service pack/hotfix/cumulative update was installed.
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability