Say I have a page with a lot of text which goes well below the fold, and want to put a link at the top of the page which allows browsers to quickly reach say the midway point to the bottom of all that text, how can I do that?
What you would want to do is create an anchor to link to the middle; <a href="#middle" title="">Go to Middle</a> HTML: And then make an anchor that indicates the middle; <a name="#middle"></a> HTML: You put the first one in say... your navigation bar, and the second one where you want the page to scroll to. You could also do this with some javascript that would take you to a specific point, but this way is more flexible should you choose to add/remove content.
Also if you did use JavaScript for this it would make you site a lot less accessible as people that don't have JavaScript installed won't be able to take advantage of such feature.