One account I deal with was experiencing disappointing ROI overall. After breaking down the search partner results it was obvious where the issue was coming http://www.blogger.com/img/blank.giffrom Google search partners.
I would swear that Search Partners were once the likes of AOL and ASK now some competitors appear. For example Furniture by CSN we would classify as a competitor at worst an affiliate at best, it is simply not the same as a consumer typing in 'Oak Furniture' to a search engine looking for Oak Furniture.
Clearly these are two different types of PPC, one is direct marketing the other more 'old school advertising'. I'm not claiming the traffic is worthless by is different and found it disappointing to see Google classify at the same thing.
On a more positive note compared to Yahoo or Bing the volume of traffic in Google just means that there is only really one player. Looking at the time I spend in Bing or Yahoo I'd be better advised to spend the time improving campaigns in Google.
Next time I'm going to comment on a post I found which gives an indication of Quality Score.