It behaves more or less the same way as an ActiveRecord (even though it is NOT a replacement for ActiveRecords). With these in mind, I proposed these patches (not surprisingly some of them where already informed issues in the rails trac):

• Ticket 7308 Addition of update_attributes method
• Ticket 10537 Addition of new_record? method
• Ticket 9862 Modificate behavior for #new (initialize) , patch not provided yet (waiting for opinions)

If this patches where applied, one would be able to seamlessly replace an ActiveRecord with an ActiveResource in a scaffolded CRUD, restful web app (I used rails 2.0.2 and the scaffold provided with rspec 1.1.1 rspec_scaffold generator. Not sure if it works the same way as "scaffold" generator on rails).