To me, Adwords provides Google a messy opportunity. I suspect there will be a temptation to sacrifice relevance for revenue, ultimately. The problem is the similar to that of running a gym, namely, the revenue stream doesn't scale with their costs. With a gym, the signup fee is a one-time deal usually, but the cost of operating the equipment (leases) is a monthly expense. With Google, Adwords may or may not scale in terms of what they can sell, but the cost of providing their "relevance" results must scale by something they can't control -- the number of pages available to crawl on the web.