Joined a club yesterday that I hoped I never would while flying a commercial real estate still photography shoot. Phantom V1.1 - over 150 flights on the airframe, 12 cycles on this particular battery. IOC Setting: Course Lock - GPS Mode. Compass calibration was performed preflight (as always, unless it's a successive battery at the same site). Waited for GPS signal acquisition and recorded the home point. Flying 200 feet above and to my left, the Phantom pitched back and took off at full speed. Remote was totally useless with any control input. Flew for approximately 20 seconds before impacting a tree at full speed. While I didn't see it hit the tree, I certainly heard it. Luckily, I found it. At the very least, it needs a new casing, new gimbal, new props, and new landing gear. And while I'll order all that today, I can't shake the nagging annoyance of not knowing the root failure. Would be interested in hearing about shared/similar experiences or thoughts on the failure.