Advertisers continue their inevitable march to accountability. Generating awareness is helpful, receiving a click through is better, but driving sales is the real goal.
Ten years ago, 90% of online advertising was sold on a CPM basis. Today that's only about a third. Instead, 45% of advertising is now sold on a CPC basis (the vast majority from Google).
But the story doesn't end here. CPA-type advertising is now 19% of spending and sharply on the rise-- this includes: pay per call, cost per lead, revenue shares, and so on.
I expect that 10 years from now CPA advertising will have caught-up with CPC (and perhaps exceeded it)-- and CPM advertising will have declined to the single digits.