Sure, I'll send you the basic functionality list that we came up with in the next few days via PC. For a short summary, we need to handle various sizes of ads and be able to track statistics of clicks, impressions and what not. For our purposes, we plan on billing a flat amount per month instead of PPC or CPI. (Advertising customers will want reports of those stats...) Other people may want that functionality of managing ads based a preset budget of PPC/CPI. I wouldn't mind funding both types since we could expand to other services. Lastly, for us, it's just one site and it's very specific to our region (Asia Pacific). We could expand... it just depends on what happens after the convert to XF.
In the end, I simply prefer a solution that will work seamlessly within XenForo instead of managing another 3rd party product.