Topshelf is a simple gnome applet which provides a place to store the files the user is currently working on (not right now, but in general, in a period of time). unlike a real shelf, however, topshelf just links to the files; it doesn't contain them.
the concept of topshelf is to contain files that are put there by the user, as opposed to the 'recent files list' which is automatically managed. for example, the top shelf might contain a story the user is currently writing; a project for school or for work, a diary, etc. on the other hand, music and video files would typically not be in the top shelf (since they cycle very fast), but they would appear in the recent files list.