I make valid (X)HTML documents that are also semantically correct. I try to use all tags as they were intended and this has yielded good results as far as my placement in Google and other search engines.
What I've been doing for the last few years is using Google Adsense as a sort of barometer to ascertain how well Google understands my content. Normally, I place one Google ad at the bottom of the page and wait for it to change. If the ad reflects the topic of my site and the text on any given page, I assume that I've done my job well and just remove the ad.
I'm wondering, does anyone else use this strategy .. and has it also worked for you? I realize that my ranking depends on many factors, but making sure the crawler could understand my pages seemed like the first battle to win.
Am I just throwing salt over my shoulder by doing this?