When you are have a nice perfect jump combo going (say 7-8) and you land on a magical platform, well, you want to jump again and again to get the points for it, also the photo's you can do it with that too ( But you already know that), I just hate it how it quits the perfect jump combo when you jump a second time on a platform.
The MPH achievements are obtained simply by surviving X number of seconds (Out of Control is obtained by surviving 300 seconds), and Death Wish is obtained by causing a certain number of sky dives (I want to say 30).
It doesn't. I thought it did at first as well, but it has to do with sky dives. Reckless Coasting has to do with crashing though (I think Dedicated is the same).