This article; How Do You Network When Your Network's All Laid Off? is getting dangerously close to describing my network. There's some really good advice about how to present the fact that you're "looking".
I'm finding that most people are very open to connecting on linkedin. I don't think anyone feels their network is big enough or diverse enough any more. Linkedin does have some very good search capabilities as well, if you're attempting to do business or gain employment in a particular field or geographic location.