On my MacBook Pro it's bad. The scrolling is jerky and doesn't feel right, like there's too much inertia and too much momentum, and you can't stop it once it's scrolling. On iOS there is to little momentum. There's also no point in it. Safari already scrolls web pages, why re-implement it in javascript? You're also losing new features OS X 10.9 does under the hood, like pre-rendering off-screen content to enable smooth 60fps scrolling. Let the OS do its job.
Yep. It's not enough to maintain 60fps (which, even in 2013, isn't always possible); if you don't want scrolling through a large amount of content to feel weird and unnatural, you really should copy the native acceleration curve, something which I have yet to see done for iOS (even Apple's own JavaScript has screwed this up). Since iOS at least has supported -webkit-overflow-scrolling: touch for years now, there's usually no point.