Fotiman - 2:10 pm on Jan 30, 2013 (gmt 0)
The vertical scroll position is the same as the number of pixels that are hidden from view above the scrollable area. If the scroll bar is at the very top, or if the element is not scrollable, this number will be 0
2. This script does not need to be a jQuery "plugin", but does require jQuery, so as long as you include jQuery first, you can put this in a regular script file.
3. That could be tricky. What if someone doesn't need to scroll at all (ie - they have massive monitor/resolution that can fit everything without scrolling)? Why not just put the button/footer at the bottom? That way, when the user gets there, they will have already seen and/or scrolled down through the content.