If you're trying to motivate other to use LinkedIn, you may find as I have that different people require different pitches to get them interested.
I find that people seeking jobs are the easiest to motivate. I show them how they can use LinkedIn to connect to people in the industries, companies, fields, and/or geographic areas that interest them. For example, a search on the keywords “Venture Capital” yields over 500 hits in LinkedIn for me.
For those not seeking a job, you can try other pitches, such as the ability to find contacts for business alliances, partnerships, sales pitches, recruiting, etc.
Finally, you can share the saying that it’s better to build your network before you need it rather than when you need it. People are much more likely to help you in your time of need if you were available for them before you needed help.