The minimap is mainly a gimmick designed to get graphic designers interested in their product, as a minimap is more applicable to graphics work. It actually takes up valuable space on the screen when working with a text file, however, since it is, as Mofi pointed out, useless on a file that would have to page down more than 3 times to reach the end.
I have numerous projects with files over 100,000 lines, with some over a million lines of code. Therefore, the minimap would be as welcome to me as a Water Buffalo in my bathtub.
On the other side of the coin, however, if all my text files were small enough to make the minimap readable, then it would just be too easy to hit page-down/page-up to get to the code I would need, and the minimap would still be useless, as the code would be small enough I could remember where everything is.