rather than "relative" links. The rel= attribute is written into an anchor element like this: <a href="page.html" rel="nofollow">Link text</a>
The rel="nofollow" attribute was introduced not too far back by the three major search engines so that blogs had a way to allow links to be submitted in their user comments and not pass on page rank -- essentially saying "this site does not vouch for the linked page", or "don't assume this link is a true vote or citation for that target page".
So the rel="nofollow" attribute was not intended as a way to channel PR around your own domain. You do "vouch for" your own pages, I assume.
Nevertheless, I also assume you could do it -- but it will also telegraph to Google that you are trying to manipulate PageRank and there's no guarantee how they will treat such an action. Matt Cutts has made some negative comments about this kind of thing, but he has made no direct "this will be penalized" statement that I know of.
Other vocabulary being thrown in the mix here is, I assume, the meta robots tag, specificaly: <meta name="robots" content="noindex,nofollow">. This will stop the page it appears on from being indexed, and it will stop the links from being followed. However, to my knowledge, Google still sees the url being linked to and even though it doesn't follow the link, PageRank is still passed to the target url, which can appear as a url-only listing.
And a third vocabuary mash up is "relative url" as opposed to "absolute url". A relative url does not contain the domain name <a href="page.htm"></a> whereas an absolute url does <a href="http://example.com/page.htm"></a>. However, both forms of url in an anchor tag will still pass PageRank to the target.
My advice would be to keep your website as natural as possible and not to worry about passing PageRank to what you consider insignificant pages. There may well be an "over optimization" flag that various practices can trip (a recent video from Matt Cutts seems to confirm this long suspected factor) and using rel="nofollow" within your own domain has a rather fishy smell to me. Besides, those insignificant pages do have outbound links to other pages on the domain, right? So whatever PR you send there still gets circulated back through the site.
My feeling on this is that it's not worth the trouble, and not worth the risk. I'd say use rel="nofollow" as it was intended -- to block user contributed links in comments from passing PR.