In a video, Google's head of search spam Matt Cutts published today an answer to the question, "Should I use rel="nofollow" on internal links to a login page?"
Matt Cutts basically said you shouldn't, but said it won't hurt you if you did. Matt said, "It doesn't hurt if you want to put a nofollow pointing to a login page or to a page that you think is really useless." But Matt said, "in general" it also doesn't hurt to not add a nofollow, and in general, you should let Googlebot crawl and explore your site.
In most cases, using a noindex may be better than using a nofollow on the link at [...]
Related Topics: Google: SEO | Link Building: General | SEO: Blocking Spiders