Models vs. Libraries (what goes where?)

[eluser]Cro_Crx[/eluser]
Libraries are used for common tasks, eg handling sessions or form validation. Models are used to handle FilIO, 99% of the time it would contain all your database calls, although if you're reading/writing directly to files then this should go in your model as well.

Models are optional, although not using them detracts from the MVC programming approach.