KenB - 4:40 am on Feb 2, 2010 (gmt 0)
I don't know if Google passes link juice on non-linked URL references, but I do know that Google follows said references unless they are blocked by the robots.txt file. My Webmaster Tools Crawl Errors page always contains bad URL references that Google picked up by reading the abridged version of a URL shown in the link text of postings by forum software like vBulletin. When I can figure out where the URL was really supposed to go I will add a 301 redirect for the broken URL to the proper URL.
As said above, making sure to have plenty of internal navigation links on pages will reduce the amount link juice any one outbound link costs you (in theory at least).