It's the elephant in the room. And for professional and job-matching social networking, there's now little competition, most rivals having disappeared in the wake of the almighty LinkedIn.
The site's only been around for just over eight years, but LinkedIn today has about 120 million users around the globe, with high penetration in Hong Kong.
LinkedIn, beloved of many - especially those in human resources - has received a generally positive reception, both despite and because of its corporate vibe and appearance.
"LinkedIn has become the de facto tool for professional networking," declared online trade magazine TechRepublic.
The reason LinkedIn works so well for job-hunting is that most of its members already have jobs. And so an army of happily employed people use it to research prospective clients before sales calls, ask their contacts for advice, and read up on where their friends and "frenemies" are getting work.
A key LinkedIn rationale is this: very often, the most talented and sought-after recruits are those currently employed. Headhunters call these people "passive candidates". The whole multi-billion recruiting industry is built on finding them. But the new imperative is to present your professional skills online as attractively as possible, and this is where LinkedIn comes in.
"You Google other people, so why don't you think they're Googling you?" LinkedIn founder Reid Hoffman asked a CNN reporter last year. "Part of a networked world is that people will be looking you up, and when they do, you want to control what they find." Hence, LinkedIn's appeal.
The site does have its detractors though. "I've not yet resigned from LinkedIn, because I'm still trying to figure out an effective way to get a really damning 'recommendation' out there for some of the total '*****' who I've encountered professionally over the past 20 years. Not nice, but it keeps me on the site," says information technology specialist Philip Wong.
But having by far the biggest market share of the professional social media market - trailed by Viadeo (35 million) and XING (10 million) - LinkedIn is evidently doing what it set out to do.
"I got several opportunities from LinkedIn that turned out really well. It opened doors for me, and for many of my friends," says Kowloon-based accountant Amy Chan, a typical account holder.