The easier question to answer is, what hasn't changed? The overall design, cockpit layout and dimensions -- same hull, same performance.
Most systems have been improved though. The newer Mirage Drive has some key changes that make it more durable and reliable. The Drive lock system ("Click N Go") is much easier and faster to use, and more rugged. The rudder up/down system is changed to make it easier (for most people) to use. Rudder tubes are more leak-proof. The newer seat has better back support. More durable bungees, better hand grips. There are some other minor changes as well (improved paddle for example). Other than that, not much. One thing about Hobie -- they don't stand on their laurels!
Oh yes, the '11 is still under a two year transferable factory warranty; the 07 would only be if somehow you were buying it new (although the '07 Drive only had a one year warranty).
If you can get a good price difference and are a pretty basic or occasional user, the '07 (if in good shape) can be a bargain. If you are performance oriented, heavy user, are going out long distances, the '11 will suit your needs best. It will hold up better against the added stresses of Turbofins.
