As far as tags - there already is a free solution thats been around forever called ICRA -
http://www.icra.org/webmasters/
and most of us use it on our sites (at least the ones Ive seen) - and its instant - you just fill in a quick form and they give you a meta to insert.
Im not sure why anyone would want to take on anything else as this system is already used by the major search engines and it works.