We went ahead and did this post on the official Google webmaster blog to make it super official, but I wanted to echo the point here as well: Google does not use the keywords meta tag in our web search.
To this day, you still see courts mistakenly believe that meta tags occupy a pivotal role in search rankings. We wanted to debunk that misconception, at least as it regards to Google. Google uses over two hundred signals in our web search rankings, but the keywords meta tag is not currently one of them, and I don’t believe it will be.
In addition to the official blog post, we made a video as well:
I hope this clarifies that the keywords meta tag is not something that you need to worry about, or at least not in Google.