Trying to understand, I don't feel LinkedIn has this space locked up the way Facebook has social locked up (plus Facebook's vision and execution seem much stronger). So why no competition?
If you compare average time spent on site in both:
Visits per user per month. Average time spent on site.
vs say a facebook, these numbers are not even close.
No doubt there is some value here and maybe linkedin hasn't figured out how to engage the users to unlock it, so if you have a great idea on how to do this you could probably move into the space and capture users (and billions).
But, the lack of direct competition would suggest nobody really has a great idea on how to do this and coupling that with the lack of hype lnkedin gets the me too clones in the space have not arrived yet ( a la groupon and the army of social buying clones ).
As for competition anyone who can create a profile page will do, FB, Twitter, I am sure there are very many.