I just discovered that Linkedin is now world’s top 20 site by the number of visitors. A year ago, it was considerably less popular and it seemed to me quite natural that a business-focused service has limited audience. Back then I thought the site would never make it to the top. Well, today I learned it did. I am not sure what the growth is driven by, but I am quite sure most of employers and headhunters check potential job candidates on Linkedin (Facebook). That said, having a profile there is a must.