There are two things that have improved my teaching since using an iPad in lesson. That is live immediate feedback and sharing written class notes.
The impact of giving good, fast feedback is one of the best returns on your time you can spend in class. Having your iPad connected to a projector allows you to instantly demonstrate exemplar pieces of work as they are created. I use a piece of software called Airpresenter which allows you to write directly over what your live camera view sees. No longer do you need to photograph it and move the pic to a different app like skitch. If your connected via Airlplay mirroring then you are able to move around the class and live broadcast the work and skills being developed in lesson.
All my chalk and talk is done via my favourite app called Paper by 53 which is mirrored up to the projector. It works well as a simple substitute to a whiteboard, but were it shines is sharing the notes as a PDF file. I use Edmodo to post it direct from the iPad immeadiatly after the lesson and it serves as a great way of allowing missing students to catch up and as homework for the occational work averse.