This is a rather long time to see a checkpoint running. Is it possible something BIG happened on that particular day?
Checkpoints occur (by default) all the time and are trigger by many internal SQL server operations.
Please check out this article, it might help you understand what is going on - http://msdn.microsoft.com/en-us/library/ms188748(v=sql.100).aspx
______________________________________________________________________________Never argue with an idiot; Theyll drag you down to their level and beat you with experience