Yes, you are right for Yahoo and Ask. Meta tags may play a minor role in these two engines. It won't hurt you to add them ;-)

Meta description are also useless for ranking. Although they are very usefull for improving the snippets in the search engine result pages and increasing clickthrough rate.

In its own «Guide de démarrage relatif à l'optimisation pour les moteurs de recherche» Google provides some clues as to what are the important things to consider for SEO:http://www.google.com/webmasters/docs/search-engi...

In English it is "Search Engine Optimization Starter Guide"http://www.google.com/webmasters/docs/search-engi...

Sorry to contradict you but meta keywords are useless since 2002. http://searchenginewatch.com/2165061

Even Google says so, here: http://googlewebmastercentral.blogspot.com/2009/0...