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.