For other companies, selling seems to be the most important issue. For Google, it is delivering the right service in the right way to the right people.

Function over fashion. Relevance over exposure. Information over advertising.

What we can learn

Google are successful because they deliver relevance.
When we get a Google-delivered ad on Google's own sites or other sites, there is some relevance to it. We don't get ads for network technology, when we are looking for gaming, we get gaming ads. That increases the chance of the ad being relevant to us and hence increases the chance that we will click on the ad.

That behaviour is what I advice my customers to nurture in their own developments. Having a huge number of page impressions (and therefore ad impressions) does not mean that you will get a huge number of clicks.
Why should anyone click on an ad when they go to a log in page? They have come there to log in, not to be diverted off your site.

Why should there be ads on a user registration page? You want them to register, don't you? Then why add another page impression with useless ads?

Think about how the site should work and give relevance to your users. Then they'll come back, then they'll be more likely to like your site, then they'll be more willing to give further information about themselves and then you will be able to target them better.
I say better, not more - it should never come to a point where once you know all about your users, you can spam them with offers. However relevant the offerings, sheer volume is a definite turn-off that will only come back to bite you. When people can see the benefit of giving information (relevant offerings instead of same volume of useless offerings) they are more likely to do so.

In conclusion

Google aren't (always) innovative - they're just better at realising ideas coined by others, going that extra mile to improve the product.

Brilliant, really.