Did you now really register to just write this post?
I registered to give someone 1.6 tutorial they couldn't recall the name of which I myself didn't even agree with or learned much from. At least he does what he loves.
Ok, this may sound hostile(I'm not) but: you will
not outperform nor outfeature Box2D, other engine might suit you better or even be better, but you will not ever do it yourself. Catto has years of experience and Box2D is tweaked crazily for performance and now blowing physics up, there is even a
huge comment discussing selected collision method somewhere in source code. You will probably get lost when friction, inertia, damping and rotation comes into equation and/or go with n^2 complexity with your AABB. Box2D is crazily packed with features really.
I'm pretty sure most of the games that use physics in flash use it judging by the sole amount of posts in it's Flash port forum(over 25% of all of it). LOVE(Lua game engine) uses it, cocos2d(obj C, popular iDevices game engine/framework) uses it, it has ports to js, flash and many more. Silly Angry Birds uses it. I'm not even sure why it is so popular, it just is. I even seen advert while looking through programming jobs once for iDevices game dev, that specifically said 'Box2D experience'.