I have a 100,000 url's in my site. Prior to the recent "update" I added keywords relevant to each page. In the last 2 weeks, I've dropped on average about 5-8 postions in the SERPS across many of my URL's. In looking at the sites above me, I'm finding they don't have keywords listed in their meta tags.
I also realize we had an "update" recently...and I'm not sure if my drop is due to the update or due to my keyword additions.
Most will agree that meta keywords have no direct value in ranking. However, google may look at them and use them as a flag to any black hat tactics. For instance, hundreds of keywords would be silly, especially if many do not appear on the page as normal text. This would be a flag to potential keyword spamming. No one knows for sure what google does with meta keywords, but many sites rank well without them. Adding meta keywords may have an indirect advantage with google, in so far as many specialist directories do use keywords and you will appear on their sites and thus have a good link.
Yeah, there were some discussions where members argued that sites can be penalized for using meta keywords. The most briliant reason someone have given was that if Google uses data mining and bayesian algos, and spammers still use keywords, presence of meta keywords may increase 'spaminess rating of the site'.
I was sceptical, but less than month ago I got very fast #1 with page I didn't bother with keywords, so the temptation is too strong. I'm trying to remove meta keywords from my most important site, part of which is ranking well, other part still sandboxed. Wonder if it will rank better or get penalized for doing such a change in HEAD section without changing the content.