I see alot of good points being made in this thread and it led me to do a little researching for myself. After putzing around awhile, I found this article which really goes into the breakdown of Technical reasons both for and against 'beneficial viruses'.
It's a bit much to read but I'm thinking it's relevent to the current debate. Anyways, I hope you guys like this link.
http://www.virusbtn.com/old/OtherPapers/GoodVir/

Note: Maestr0, cool thing about this article is it uses many references from Fred Cohen .