I do not know all the ins and outs but this is very helpful for people that like Google and know enough about websites to know tagging is important. Google has several options to help with progressing a website.

With http://www.google.com/trends you can type in a key word and it will show you its national ranking. With this you can pick the best tag words available. You type in a word and Google trend lab produces a graph over several years showing the highs and lows as well as other close related trend words.

Another good tool from Google is there Web Master Tools This can show you when a web sight was crawled. This is easy to use, has lots of explanations and is easy on the wallet. http://www.google.com/webmasters/start/