Just some thoughts on my surfing experienced of late.
My sites serve adsense.
I was surfing for a product out of town and found it, but also found they had adsense ads with a link to an accommodation. I booked the accomm. for the business trip to see the product.
Next example was looking for a new host, searched google, searched for particular host names and noticed that competitors must have their competitors in keywords to be shown at the same time, good idea. Anyway I found a new host, after searching, reading reviews, and it all came through googling.
I'm using adwords, just lightly at the moment, because everytime I turn it on, I get a nearly instant response and we're only a small company and cannot cope with tons of work all at once.
Our sites do show adsense ads that could be possible competitors but there's plenty of work for all of us, people just need to find as many options - hopefully finding and considering us amongest their search(es).
Google/adsense/adwords is a very powerful marketing mix and easier to budget and plan for.