I’ve been messing around with mini maps, and after a few different approaches, I have come up with a cool demo that simulates a radar screen. The screen even has a sweeping beam that lights up the blips, which fade over time. Only instances which inherit from an object called oMappable are drawn on the radar. The size of the blips is based on the width of the sprite of the oMappable child, so objects of differing sizes will be shown in scale relative to each other.
It runs quite well, with up to 4000 simple objects (~30fps on a 2.0GHz Core2 Duo).
Demo (.zip)
Project Source (.gmz)