I liked the down-to-earth tone and the audacity to say that an organisation might decide not to use social network sites. Some of the situations your organisation might find itself in:
- You're still trying to get a handle on basic software infrastructure
- Your target audiences aren't using social network tools
- You don't have time to experiment with something that might not work
- You're not willing to deal with technologies that don't work as well as they could
- You're not ready to invest in gaining a real understanding of the medium
- You want clear editorial control over your brand and message
I think I would put number 5 as number 1. If you want to explore whether or not to invest your time, try understanding social networks and their cultures.