SharePoint 2013 has a lot of new Developer Changes.Apart from the new App model a lot of new classes and namespace has been Introduced to program with the new Social and new Event Receivers.
See the Developer Samples SharePoint 2013 Developer Tutorials and Samples
Other Developer Training Videos -
SharePoint 2013 Developer’s Training Videos – A collection of SharePoint 2013 developer Training Video’s
A Good Introduction to apps – Learn more about apps for Office and SharePoint by watching 90 second videos.
Introducing the app model for SharePoint 2013 – A good Info about App from developers Prospective.
Requesting and Granting Application Permissions in SharePoint 2013 – How permissions are needed for Apps to work in Cloud.
SharePoint 2013 workflow architecture platform overview - Improvements to workflow,What’s New and How to build workflows in SharePoint designer and Visual Studio.