I think you should have meta tags on every page, but if all the pages are about the same subject matter, then just repeat the same text.
It has been said that Google takes less notice now of what is said in the meta tag, but you still need something there.
I have noticed with two new websites of mine that it isn't the homepages that have been first linked on Google, it's other pages, so there needs to be a description in a meta tag to show in Google for the pages that Google just happens to show first in a search.
Code downloaded to my PC will be deleted in due course.
WIN7; IE9, Firefox, Opera, Chrome and Safari for Windows; screen resolution usually 1366*768.
Also IE6 on W98 with 800*600 and IE8 on Vista 1440*900.