right now I just have 2 running but have 4 more et up, I just have to do a little tweeking of the code and get some sites added. Honestly how quick the list grows and what kinda traffic it produces depends alot on how people send traffic and also the niche. I could force 1000 hits from one of my sites but if its all blind links then most of the hits are not gonna click anything so that makes it look like people are sending a shitload of hits and not getting anything in return, you can look at the numbers here and see what I mean
http://www.bootporn.com/autorank/autorank.html
Babes in Boots sends alot of traffic but from what I can tell 99% of it is skimmed traffic so the productivity is low.