My very first experiences with online networking were already in early 2004. The very first online network I discovered was LinkedIn, which started up one year earlier in May 2003 as a very formal online directory for business people.
In those very early days LinkedIn already had about 20.000 users in Belgium and 1,6 million members worldwide. Among those early adopters I stayed on top of the ranking in Belgium for almost two years.
Today LinkedIn has hit the 50 Million users marker ... 50 million business people worldwide can now be found on one large network.
From the very start LinkedIn always had one outstanding feature. Whenever you are looking to get in touch with someone, you will search for his or her profile and immediately you will also see which people you have in common in your networks. An introduction by someone you know is just a small step away.
Of course LinkedIn also changed over the years. I saw them introduce paid accounts, offering much more options which can be very useful for some users (e.g. headhunters !).
More recently they also introduced applications which can help you to build your credibility.
The best example for this is the SlideShare application which enables you to add Powerpoint presentations to your profile.
Even today LinkedIn is still known as the "Yellow Pages" for business people, the second spot (after Google) where people are going to search on your name. They became the reference website for business networking. This should already be reason enough for everyone to have a profile on this platform and keep it up to date.
Excellent tips on the use of LinkedIn can be found in Jan Vermeiren's great book 'How to REALLY use LinkedIn'.