I just now needed this to replace a bunch of objects with empties so I can use “Dupligroups” in stead. I thought I’d publish it… but no more info for now… perhaps later. It’s meant to work in Blender 2.5
Download it here: ConvertToEmpty_1
Now Blender 2.5 still isn’t stable so don’t expect it to work as is forever… I found it usefull though.