msafi - 5:54 pm on Apr 10, 2011 (gmt 0) [edited by: msafi at 5:58 pm (utc) on Apr 10, 2011]
No, comments 1-5 will move up the pages as more comments come in. At first, comments 1-5 will be on http://example.com/foo/. When 5 more comments come in, 1-5 will be on page-1. After yet another five comments, they'll move to page-2, etc...But that won't cause any SEO damage. There will be no duplicate content. The engines will just have to update their data -- like they have to do with all other dynamic sites...
EDIT: No I think I'm wrong here. They'll remain on page-1. Newer comments will go to page-2 and page-2 will be displayed before page-1 in pagination.
[edited by: msafi at 5:58 pm (utc) on Apr 10, 2011]