"rel=nofollow" attribute for non-content links

For a true SEO of punbb, which goes past the frivolousness of the SEF URLs, there is something which I was convinced was implemented already, but actually isn't.
Having search engines index "junk" on your website is not productive; by "junk" I mean everything which is not content related, for example the login page of the forum, or the subscribe "popup" page.
Those do not even need to have a SEF URL, they should not be visited by search engines at all.
Adding "NOIDEX" in a meta tag apparently has no effect other than on private implementations of google search, so it would definitely be a good idea to have all links to "not content rich" pages ignored via a "rel=nofollow" attribute.
Example:

<a href="[...]/punbb/login.html">

becomes

<a href="[...]/punbb/login.html" rel="nofollow">

This same thing should be done, as previously stated, for "service" links, login/logout, subscription/unsubscription, search, and all the lilkes.
Maybe it doesn't really help significantly with search engines, but I see a lot of "elegance" in the PHP code of punbb, so there is no reason to add even this one more bit of "delicacy" to the source