It is late so I will keep it short. I just launched my Simple Learning Tool Interoperability stuff. It is all up on the Google App Engine at:
http://simplelti.appspot.com/
It includes a test harness, developer documentation, and sample code in Java, php, perl, ruby, and python.
I also have a fully functional Sakai Tool that fully supports the Simple LTI protocol.
Probably the best place to start is the developer documentation.
This is kind of the kick off for the IMS/Sakai Google Summer of code stuff – I tried to get a head start.