I'm wandering down this very same path. We host our website with Squarespace and I want a simple form that creates a lead in Sonar. While I can enter markup or code into Squarespace, I am not a JSON expert and need a basic starting point to build this. I have read through the REST API wiki and while it looks totally possible, there are no real world examples that make sense to me.
Anyone built this type of form and want to share the code? Just need to capture name, address, email, phone and a spot for notes (where they can type in desired speed, etc). Or I create some custom fields that can capture speed, referral, etc. However, I want to get away from capturing everything in a Google Doc and then re-entering it in to Sonar.