What if I have unique meta description for every page? It's better for every page to have it I think.

A search engine results pages (SERP), is the listing of web pages returned by a search engine in response to a keyword query. The results normally include a list of web pages with titles, a link to the page, and a short description showing where the Keywords have matched content within the page. A SERP may refer to a single page of links returned, or to the set of all links returned for a search query.

Which Meta Tags Should You Use?

For Google adding the Description Meta Tag won’t result in a boost in the Search Engine Results Pages (SERPs), but the description might be used for the description for your SERP listings in Google. So though you won’t get a ranking boost, if your write an interesting Description Meta Tag and Google uses it (not guaranteed), you might get a higher click through rate compared to a random snippet of text from your pages. All other meta tags (including the Keywords Meta Tag) are either completely ignored or won’t result in a SERPs boost.

Yahoo says they use the Keyword Meta Tag when it ranks a page. So it makes sense to add one for Yahoo and any other minor search engines that still use. Also there are directories and other websites that automatically take this information to create a listing to your site. Don’t fret over it though, add the main phrase for that page to the Keywords Meta Tag and user friendly description of the page to the Description Meta Tag and forget about it.