I find Google ad placement increasingly annoying as the advertisement delivery seems not to be at-all in keeping with the site content on my pages or on the blogs.
More often than not I have technical articles and posts which would benefit from ad placement pertaining to the subject. For example someone reading a technical blog might actually be more interested in buying software components online than ordering a pretty Fillipina girlfriend. (well, you're supposed to be at work after-all)
Google would therefore benefit a great deal by enabling subject hinting on the sites that would allow a webmaster to target a proportion of the ads for a certein genre and which they could then "pad out" with the other inconsequential and ridiculous bla bla that they seem to be serving these days.