Outgoing links to penalized sites may harm your Google Pagerank
Be careful to where you link. External Websites with a Pagerank of 0 may have been penalized by Google. Linking to them may cause your own Pagerank to drop!
Incoming links from penalized sites do not harm your Pagerank
Don’t worry, if penalized sites are linking to you, that’s not harming your Google PR in any way, which I assume is reasonable, considering that a webmaster has no influence on who is linking to his site externally.
Google Pagerank and Google PR are registered Trademarks of Google Inc.