SEOs tend to debate this pretty heavily. Even among the pragmatic [read: I'll do anything to get rankings ;) ] SEOs, some people claim it's better to hoard PageRank and some people claim it's better to "look like a real site" and point out that real sites tend to have outlinks.
I lean more toward the latter school of thought. If SEOs go to extremes trying to recreate or mimic the content/linking patterns that "real, useful" sites have, before you know it--you actually end up with a real, useful site. :)
I'm mildly joking here, but the rule of thumb that I'd go with here is that visitors to your site probably want to know about useful related resources. And the higher-level principle is to make a useful site that visitors consider a good resource, want to return to, and would mention to their friends.
A quick example: I was recently reading about a program called KCeasy on Slashdot, so I checked out their website at [kceasy.com...] If you visit the site, notice that they have useful links to giFT (the underlying protocol) plus other various giFT clients. This is a non-commercial site that's just trying to give info on their piece of software and that gives info on other options as well. That particular site would be much less useful if the author tried to hoard PageRank or somehow keep every visitor on their own site. Instead, the links are as useful as the site itself. It's a good site; the sort of site that sticks in the mind of an interested visitor.
So that's my personal take. Bear in mind that I'm of the "build the good site, and the rankings will follow" school of philosophy. Other folks may belong to the "get rankings first, and then develop the site" school of thought. I'll step aside to let someone from the pragmatic school of SEO give their take.
Added: Here's another interesting non-commercial site: [placelab.org...] The idea is to offer geolocation by mapping WiFi hotspots to GPS readings, e.g. by wardriving. It's a really really neat site: there's publications, lots of info, and even a place where you can upload your wardriving logs to help the project out. But would the site be helped by adding a few additional links to describe how GPS works, how the NMEA standard allows your computer to talk to a GPS unit, maybe a link to geocaching.com, NetStumbler, or other fun tricks that you can do with GPS or WiFi? Yeah, I think that would take a really nice site and kick it up even a little more.