It's all the user. I run without anti-virus and the last virus I got was in 2004. Just keep a firewall and don't go to random websites and download sketchy files.

There was mention of being able to IM across games, to anyone on battle.net. Is there any possibility of being able to message friends on other instant message networks gtalk/aim/steam?

no torrenting, but many shows like NOVA are just online. http://www.pbs.org/wgbh/nova/programs.html theres a few episodes, check out the rest of the PBS site, many of the science shows are downloadable.