ave you noticed that the Google ads on GMail beside your messages are extremely relevant. So, somehow it analyzes the content of the mails on the fly and presents the ads. The ads on blogs, on the other hand, are often irrelevant unless your blog has a focussed content (technology blog, marketing blog etc. etc.). Now, this is not fair. And if blogs have to be so specific their beauty is lost, even if they are better repository of knowledge that way. Specific, focussed blogs can not be adopted by everyone, it does not make sense either.
Keeping this in mind, I think google should think about making some changes specifically for blogs so that if the ads are placed on post pages, at least then it shows ads relevant to the post. The next step would, of course, be that ads are relevant to the content of whatever page one is seeing (main page, post page, archive page), if it is not on posts page (e. g. in the sidebar or the footer).
This will improve the efficiency of this medium of ads highly.