I recently quit my job and have taken a few weeks to decompress. The first thing I did with my down-time was port Arducopter to Flash so I could do development and tuning in an environment that was more developer friendly, faster and fun. This app has real-time plotting of most system variables, almost all AC functions (except mavlink) and repeatable situations so you can tune your quad.
It's a great tool for understanding the actual behavior of Arducopter. I know I've learned a lot. Each sensor is modeled to include noise and delay to ensure accurate behavior of the system. Under the hood, the SIM is running at full rate and all of the timers are stepped in a way that each flight is repeatable. Even the wind will repeat exactly with each run.
I'm also taking support donations to help offset my many many hours spent on this tool. I hope you like it and I hope it helps you fly safer and save a few props.
Arducopter Sim will live at http://www.jasonshort.com/ for now.