Are you talking about changes to the sites that you link to that are beyond your control? If you think that a site might potentially change to include something you wouldn't want to link to, don't link to it. Period.
I had a PR2 on my links page.. Then went and redid it and removed a few links that didn't keep mine up and so on... Next thing my PR was gone... I have no idea what is going on, however I did loose a few other PR's on other pages too. (maybe because I redid them too!)
I think to take off outbound link from your site should not effect your PR.
But if other take off your link from their website (inbound link) that will definitely effect.
Other is about the content of your page, if it's the real unique, no one copy you (which you may not know, use copyscape to check it) then it should be ok for page rank. Oh, one more. Make sure that you didn't link to any dodgy or spammy sites as seogoat said.