According to ZD Net, Free Software (Linux et al.) may need to be worried about pirated copies of commercial software.  Apparently your average user would prefer to run an illegally obtained copy of a commercial application than run legitimately free software.  There's an interesting discussion on this here.  My thinking: it doesn't matter.  Linux isn't terribly concerned (yet) about home market share: the business place is where it really excels.  The lack of games and completely legal MP3/DVD/etc. implementations is a bigger hindrance to Linux at home than the availability of pirated copies of Windows.