I've been trying for a couple of days to change one of my Adwords display campaigns from CPC to CPM, but I've been unable to find a way to do it. Any help?
I would not do that myself but it's in the campaign settings. Look under Bidding and Budget section. Select the last radio button, Focus on Impressions.
Personally, I have found that CPM can be excellent. But it's all in the details - test, test, then test some more.
CPM campaigns can work well and save money once you have established your CTR. But I'd test with CPC first.