I think I chose Internet technologies.

I've been an active member for a year now and have been very successful with it. You need to join some of the membership groups to get real benefit and get to know the people you are linked to. I would be one of the highest linked VAs at LinkedIn (number 4 I think) and have been able to do podcasts, gain new clients, get new team members, met people when travelling overseas, and found new resources for my business, all through LinkedIn. One of the best discussion forums has over 5,000 members and is very active - it's run via yahoogroups.com.

My profile is http://www.linkedin.com/in/kathiethomas and you should be able to see all the groups I belong to there - I don't participate in daily chats with them all.