In addition to family on Facebook, I use the Timeline as my own personal photo album and life experience audit log. Most of the things I add on Facebook are set to "Only Me" to prevent spamming my contacts.
In addition to being able to find new career opportunities, the LinkedIn engineering teams have implemented a news feature which is curated by your own connections, as well as, "leaders of today" -- whom are successful executives of startups and large corporations.
The more connected you are at a professional capacity -- the more career opportunities start to emerge. More doors, more possibilities, more challenging problems to solve, more people you can make a positive impact on, more chances you'll have to prove your leadership, integrity, and expertise.
Since you're able to follow anyone that has valuable information to you, you're able to customize your feed based on your interests, passions, industry, and more. This is a different model from Facebook because Facebook requires a handshake and usually you're connected to people from high school who don't share the same interests.
to make the world a better place. Not only do we get to help each other with projects, we also get to share an infinite amount of knowledge over how to solve complex software problems. Every software engineer and team has a unique way of solving a particular problem space -- these techniques and approaches become completely transparent on Github. Originally, Github only supported open source projects but with a rather large investment of $100 million, they are now tackling the enterprise arena.