To date, I have yet to see anybody find a way that Yahoo actually uses the keywords meta tag (I am sure that as soon as I post this, somebody will post a link to prove me wrong)
I kept asking myself, "Why would Yahoo invite spam?"
Then the answer struck me. That is exactly what Yahoo is trying to do. By requesting the keywords meta tag, Yahoo is saying, "Please provide a list of search terms you'll be spamming us with so that we can penalize your site."
Of course, this might be just my imagination gone wild, but let's say a site comes up on a search for "lunar potatoes" (Believe it or not, Yahoo found 34,200 such sites!). Yahoo would then check if the term is in the keywords meta tag. If it is, it might run some additional diagnostics, such as keyword density, identical inbound links, etc. If the site fails certain criteria, Yahoo might do one or more of the following:
- Remove the site from the SERPs for that search
- Relegate the site to the end of the results
- Place a dampening factor (penalty) on the site for that search term, perhaps even responding to the extent to which it failed the spam test
- Place a red flag on the page/domain, so that the entire site can get easily banned if it accumulates red flags for too many search terms
- Do nothing to the site, but use the data to better understand how they are being gamed to keep ahead of the optimizers