That's what I've always thought. Those programs that make you include a disclosure page or insert special code don't seem to get it. By doing so you're really flagging to google that you take paid posts, which could see them drop your PR, which in turn limits the number of opportunities you can take.
PPP really pi$$es me off like that. Their opportunity system is all built around PR (ie. the higher your PR the better more expensive opps you can take), yet by participating you may very well cope a google slap and lose your PR. Makes no sense to me.
I joined PPP but never used PPP because I can tell a blog who is doing paid posts by looking at their first page. Most paid opps always have three links in them with different keywords. It's easy to spot a paid post because they don't have a natural linking style and why would a blogger link three times to a site using different keywords unless they are getting paid to do it ?