Let me add something here.. speaking specifically about AdWords..
Efficient PPC is a program that is used to build long-tail keyword campaigns. The campaigns are broken up into extremely tight adgroups. I'd assume that if you're cranking out X-thousand long-tail keywords, you're probably going to focus mainly on phrase and exact match, and then maybe let broad match pick up the slack.
However..
You should know that if you already have a successful broad match campaign running that is showing ads for the keywords that would be included in your long-tail list, there's no guarantee your phrase/exact match campaigns will capture that traffic from your broad match campaign.
Ideally, and according to Google, a query will trigger the keyword and ad in your account that are best targeted to it. So if you're broad match bidding on "gay webmaster" and phrase/exact match bidding on "best gay webmaster forum", the surfer who searches for "best gay webmaster forum" will see your phrase/exact match ad.
In some cases, though, if you have an established campaign that is already capturing these queries and it is performing well, your new long-tail campaigns will capture only a fraction of the impressions they should be receiving. Part of it has to do with quality score, but that's obviously not the only metric involved since your long tail campaigns (if properly formed) should have great QS. I think the other part is based on performance history, which ties into quality score as well, but isn't something you can just view in your campaign manager.
So the decision is then: Do I pause my broad match campaigns and allow my new long-tail campaigns to get some play in the hopes that they will eventually cost less? Or has the success of my broad match campaign driven my CPC low enough that the long-tail campaigns are not worth it?
Anyway, just food for thought for when you run into this in your campaigns.
