Hey guys, late to the conversation but good info anyway. I have accounts with various social networking sites and have played around - they are tools. None are the silver bullet. There are great ways to use the tools though - some swear by LinkedIn.
Whatever networking methods you incorporate, I'd suggest a personal relationship management tool to help you keep your relationships organized. This is something that YOU manage, privately. It could be ACT!, Goldmine or my site designed specifically for career management (not necessarily sales):
JibberJobber.com.
I designed JibberJobber in my own transition, realizing the value of the relationships I was creating during a job search. There is a free version where you can have 250 - 325 contacts - I encourage you to check it out and let it complement all of the social network sites as well as help you manage contacts from offline (gasp) face-to-face networking meetings.
For small businesses, I use JibberJobber for my marketing - after all, isn't it all about relationships? Feel free to get a
free account and let me know what you think.