I use an include file for the metatags. Do I put the keywords meta tag at the top of each page of my website or just the homepage?
Forget about meta keywords tag. I mean it. It doesn't matter. It has no value. Google doesn't read it and it doesn't influence your rank in any way. Don't bother. What was the purpose of saying that? Increasing your post counter? Spam is bad. Value is good.
Has this always been the case? In researching this question I found quite a few folks saying to add keywords to metatags. Obviously, the bulk of legit information said to forget it as Google doesn't read it, but I just wondered if maybe Google read it at one point, then stopped.
Those folks are cheating themselves. Google never considered meta keywords. http://googlewebmastercentral.blogspot.com/2009/09/google-does-not-use-keywords-meta-tag.html There ARE meta tags that Google considers (see the link), but that doesn't apply for meta keywords.
Put all keywords not on same page. First your most target keyword on home page, after used all related theme base page.
In early 2010 Google has made it clear with Blog posts & videos that they are no longer checking Meta Tags. Don't waste your time optimizing for them.