Planet13 - 10:27 pm on Nov 10, 2010 (gmt 0)
This may be a simplistic view, but...
If a page is relevant to one of my pages, and the page makes me say, "Man, I wish I had written that," then I will link out to it with a followable link.
I do this with one site that has a large directory as well as with my main ecommerce site.
On my directory site, all the links are free and followable - I don't even require a reciprocal link (I do suggest a reciprocal link, but it ain't required). But I do require that the page I link out to is on topic, helpful, and isn't a direct competitor of mine.
Again, this might be overly naive, but I think that is the way it should be done.