One of the problems with Lion’s scroll bars is loss of context for how much content is in the window; unless you pay attention while you scroll, you have no idea and no way to tell where you are in a document. In the Messages beta, Apple provides an example of how developers can handle this loss of context. Just above the text entry area, there’s a clear overlap of the text entry with the content when it is scrolled off the bottom.
As ever, Apple has addressed the details too. The indicator is subtle and fades at the ends. Moreover, when scrolling, the indicator fades in as the first several pixels scroll by. Most users won’t see this, but when scrolling slowly, you see the attention given to this aspect of the experience.
This isn’t a panacea, but it shows that Apple is thinking about some UI issues that are endemic to Lion’s iOS-ification and solving them in new and exciting ways.