I don't think so... I don't think YPN has specified a max. Just don't overdo it though, not good for your visitors.
Yes, there is a 3 per page max. Just call their support, they tell you 3. If its more than 3 its considered "excessive"
There's no point in putting more than 3 anyways. One of YPN's annoying aspects is that they repeat the ads if you have more than one ad block on the same page. Very, very lame of them.
I just got a response from YPN about this... "We do not have a known limit of ad units per Yahoo! Publisher Network account. If your question is per page, we would suggest to limit the number of ad units to 4."
Uh so what's with the different response " Yes, there is a 3 per page max. Just call their support, they tell you 3. If its more than 3 its considered "excessive""
Different responses could be because different people from YPN answered and I would guess there is no set-in-stone answer yet so they are just saying what they think.
I dont know you, but when I land on a site that have more than 3 ads blocks I think it's a "made for ads clicks" and leave.....