I keep revisiting this idea myself. I figured a suitable prototype would just let you :

* Create a profile.

* Record where you've worked.

* Post small "updates". Which would be visible to "connections".

That would be the core of the service and the job-hunting stuff would be kinda-seperate.

The problem is twofold: scaling and getting users. If you have no users then the system is futile (I setup a dating site once, which struggled due to lack of users. You join? No users in your city? Never return). On the other hand if you suddenly have 50,000 users you system will struggle if you're doing it on the cheap with a simple virtual machine. You need to plan for rapid scalability but assume you'll get none.