OSX Lion hides scrollbars while not in use to make it seem more "slick", but at the same time the issue you addressed comes up: people sometimes cannot see whether a <div> has a scroll feature or not.

style.css

::-webkit-scrollbar {
    -webkit-appearance: none;
    width: 7px;
}
::-webkit-scrollbar-thumb {
    border-radius: 4px;
    background-color: rgba(0,0,0,.5);
    -webkit-box-shadow: 0 0 1px rgba(255,255,255,.5);
}