Some of the MVC mantras:

• Keep models fat, controllers skinny
• Keep as much business logic in the models as possible
• Models should not talk to view

Controller stinks if:

• The controller services too many requests (i.e. has too many actions)
• The controller has domain logic (i.e. model code has crept into the controller)

What a controller should not do:

• Bind post data to view models – use model binders for this
• Calculate something (domain logic) – view models or entities should do this
• Validation – best if view model validation is handled automatically (using binders)