I think that Active Record is an overused pattern that encourages mixing business logic with the persistance code. It doesn't do a very good job of hiding the storage implementation from the model layer and ties the models to a database. There are plenty of alternatives (described in PoEAA) such as Table Data Gateway, Row Data Gateway and Data Mapper which often provide a better solution and certainly help to provide a better abstraction to storage. Also, your model should not need to be stored in a database; what about storing them as XML or accessing them using web services? How easy would it be to change the storage mechanism of your models?
That said, Active Record is not always bad and is perfect for simpler applications where the other options would be overkill.
