OSX Mountain Lion is starting to fall for this trap by hiding scroll bars. When I need to scroll, such as dragging the slider up/down, I can't even tell where it unless I first do a dummy scroll. This is retarded..
Just on that I use the touchpad with two fingers on my Macbook with no regard or awareness of what is now to me a redundant control, I don't need to know where the scroll bar is at, I just push two fingers in the direction I want to go. The absolutely effortless, intuitive and completely position agnostic (of my two fingers) behaviour of the touchpad is a marvel to use and one of the reasons I could not consider other meritorious hardware / software computing solutions... and the recent (Lion I think) flipping of the page scroll action direction was another good idea too... guts and design sense, and free koolaid. Sip... mmmmmm
"Take that, you hostile sons-of-bitches!" -- James Coburn, in the finale of _The_President's_Analyst_