meta tags are not as highly used by search engines as they used to be.. Your best bet is to use a LOT of descriptive text on your site (too many images kills your site) and to have search engine friendly urls (meaning no session ids like with most shopping carts)
the other thing that is MORE important now than meta tags is rank. The google and alexa rank bases the importance on your site on how many sites backlink to your site.. So the more outside sites that have YOUR link on it, the higher your page rank.. thast why sometimes you see spammers just post LOADS of links on a forum.. Blogs are another way of people to backlink.. Lots of people offer allifiate links programs where you set up a page onyour site and trade.. I'll post you if you post me type of deal..
Certain backlinks have a different level of importance, and the actual algorithm that google uses is a mystery.. but they have it down, and that is a LOT more important than meta tags now adays.