I don't make money in mine i use it to help the people that come to my website. guess if i had a higher pr i could charge some of them. But i don't think so.
I think that a good business takes time. I am sure that those who have high PR ranking and high traffic, they make money.
I was suprised at how many directories there were dotted around. I own a directory of about 3 sites Just never bothered populating/promoting it. Too many other things to do. I do know an owner who makes a small amount for his directory ... meaning a few hundred dollars a month. Not met anyone who has above that although I can see it being very possible with more traffic and quality.
Still kind of building up the foundation on the directory, so can't really put a value or ROI on it yet. Hopefully it will get indexed really well and becomes an authority, then expand from there.