Outside of tech circles, I don't think it's a particularly useful business/productivity tool. At most, it's just a bit of fun. I personally prefer to keep my "social networking" to a minimum, as it inevitably impacts upon my work. My methods of communication:
- Email (both business and personal)
- Facebook
- Telephone
- Snail mail
- SMS
I block/ignore all other methods, including IM, Twitter, Pownce, etc.