First, they have to find a company with their kind of niche. Second, they have list of companies that implement adsense. Third, they have to outbid the big guys because they have large budget and Google won't show low CPC over competitive ads. Fourth, they have to check over time to make sure they've not been dropped or removed from the site. Fifth, they still have to watch the ROI from CPM as you would for CPC.
Fraud from CPC doesnt eliminate it by switching to CPM.
As an advertiser, there's no dramatic changed and I'd stick with CPC over CPM.
[edited by: asianguy at 8:50 pm (utc) on April 28, 2005]