Show document tags in right gutter
Eclipse has a really useful feature (once you know it exists) where it has a gutter on the right which where it displays various areas in the document. An area is drawn using a box filled with a color. Examples of this are areas where a file diffs from the one in CVS, compile errors in a Java file, location where a match was found during a search etc. The top of the gutter (on the right of the top scrollbar bottom) indicates the top of the document. The bottom of the gutter is the end of the document. You could also use this for displaying a fold region.
One obvious use in gedit would be when searching for a string in a document: instead of pressing the Next button or Ctrl-G until you've found the match you're looking for, you can see all the matches in the right gutter and simply click on one to jump to that location.
Another use for this feature would be to show bookmark locations.
VS.net does it a little different. They show the gutter on the left *inside* the ScrolledWindow. Disadvantage is that you can only see/click items currently visible in the viewport. (the yellow line here indicates new code since the last compilation)
Finally there's this idea from the Evince guys: