Good point. However, even if times get tough for Google, the basic principle (a large number of advertisers that trust them are worth more than a smaller number

Good point. However, even if times get tough for Google, the basic principle (a large number of advertisers that trust them are worth more than a smaller number of referrals) still stands. For Google to start screwing their advertisers, times would have to get so tough they'd want to throw their entire business model overboard. Somehow I doubt that will happen. (and I say this as someone who's not particularly fond of Google to boot)