If you're a social and professional networker, LinkedIn is a great company. Through their service (which is free for the basic member), you can connect with dozens, if not hundreds, of people through your extended network. I've also found it to be of excellent use for simply keeping up with people as they move around different jobs or change emails. In addition to this, LinkedIn has a number of Yahoo Groups, including LinkedIn Bloggers and LinkedIn Sales, that help optimize your use of the program or simply to discuss various aspects of it.
In any case, if you're a LinkedIn member, please feel free to send me an invite if you're reading this. My profile is publicly available at https://www.linkedin.com/in/pmesritz.
Its also great for Marketing — you can figure out who to talk to with a little bit of research.
