I have a friend who calls LinkedIn "a rolodex that other people keep up to date".

There is some value in posting on LinkedIn, but the real value is that you can go back and find people who are weak connections when you are looking to hire, purchase services, or ask favors.

I think everyone should join LinkedIn and connect to every one of their colleagues that they would work with again. Then, once in a while, keep that connection alive by sending a message or commenting on a post.

It's a long game, but will pay dividends should you ever need to chat with them.