Starting with Lion, a few of the Apple applications (like Safari and Mail) have some iOS like features when it comes to scrolling. If you've ever used an iOS device you'll find that when you are scrolling around and come to the end and scroll past it, it will scroll but once you release your finger, the screen will jump up or down and stay at the top or bottom.
Lion and Mountain Lion continue this trend. However, the jumping is more of an cosmetic thing and should just stop at the end. So Chrome, for example, will just stop scrolling once you reach the end with, but Safari will pretend to scroll and once you stop trying to scroll further it will bounce back to the end, but the end result should be the same, you should be at the end of the page. If that isn't happening, then that's a different story.
As far as reading and highlighting text goes, that's most likely because you have user accessibility enabled and it's reading thing aloud. Go to System Preferences->Accessibility and turn off the voice-over feature and see if that makes it better..