Meta description bigtime! On Google search results the blue link text is the site's title tag then below it is the meta description text. It's one of the most important
SEO attributes.
As for meta keywords, Google doesn't both with these. In the old days, when search engines were mostly crap, people used to do what's known as meta keyword stuffing, putting ridiculous amounts of keywords in so their site would show up for as many search terms as possible.
Such a situation was anathema to the Google guys, so when they arrived on the scene they decided not to apportion any importance whatsoever to meta keywords.
Yahoo used to, but stopped. Bing, who've just taken over Yahoo's search function, allegedly apportion a teensy-weensy bit of importance to them but that's all.
Other search engines too, may also apportion importance to meta keywords and whilst they may not be the biggest players on the scene (for example the aforementioned Scrub the Web) they none the less get regularly indexed by the big boys.
In the end my feeling is this, yes, meta keywords are possibly the least important aspect of
SEO but you might as well add them anyway, firstly for the sake of being thorough and secondly because you've nothing to loose by adding them except maybe five to ten seconds of typing.