I love how OS X/iOS scroll bar disappear. You know from the content you are reading where you are on the page. It's very, very rare (probably never) that I am lost on a page and I have to scroll slightly up/down to know where I am.
Also, isn't the scroll bar really useful when you need to scroll up and down the page quickly by an arbitrary amount?
I expected someone asking about scrolling an arbitrary amount. After all these years of reading internet articles and pdf manuals on Mac/iOS, I've rarely ever encountered a case where clicking the position on the scroll bar beats the speed of flickering the trackpad (and that's even excluding the precision). In fact, there's rarely an internet page where I can't get to the end within one flick.
http://www.theverge.com <- this is one flick
(While we're at it, yes, you can still drag OS X's scroll bar if you really want to. I've used it for pdf manuals).