I just tried it (again) over the weekend. First the campaign runs like never bevore, I had to set the daily campaign limit 2 times higher at the first day. Second day still good, but after 48 hours first the keywords with the most clicks (in the best adgroups) get the highest cpc, then all the others, too. The given reason: landing page quality score. Of course I tried different things at the landing page, too, not only a new domain name, more content and so on but nothing helps.
Since this slap came last month I advertise with yahoo, too, and it is working a little better every day but at the end I think it will be only about 10% from the adwords traffic volume.