Adsense always seems to show relevant ads on my sites. Of course I alway laser target my content to what I want it to show.
Depends on the site. My genealogy blog isn't exactly optimized because I just do it for fun. I wrote something about cemeteries recently and got a bunch of ads for funeral homes and memorials. Other sites get near 100% relevant ads.
I think most of the times ads are relevant (almost 90%+). Adsense has perfect senses to smell the content and show relevant ads,
all match the site content or relevant topics - most match the page content - all together always a 100% match always interesting for my site visitors - nothing at all to complain i am fully happy with adsense delivered
I agree - same with me; you've got to optimize your content to give Google something solid to work with.
I'm quite unlucky, I suppose - on my site, I get relevant ads maybe a third of the time to half of the time. It's quite disheartening.