LinkedIn is focused on helping companies find and recruit employees, and also helping job-seekers find new jobs. Facebook at Work seems to be focused more on communication and collaboration within a given company or project.
Of course, it's entirely possible that Facebook at Work would grow into something closer to LinkedIn. Despite LinkedIn having a huge head start in this area, Facebook probably could catch up. Lots of people already have Facebook accounts, and people generally like having fewer accounts for things rather than more. Plus, Facebook could easily replicate a lot of the recruiting features that companies currently pay LinkedIn thousands of dollars per year for.
1) Ads 2) Enhanced subscriptions for recruiters 3) Premium subscriptions for end users
They are a social network for professionals, companies have a profile, people post resume stuff on it, recruiters use it to find people for contracts or jobs.
I have people visit my profile, but I can't see who they are unless I pay a subscription.
I list Visual BASIC 6.0 as a skill and there is still a small demand for work with it in legacy software.
I get all kinds of LinkedIn email from groups I joined, some of the email is basically spam and makes me want to quit the group. I made a message filter in Thunderbird to move all LinkedIn email to my LinkedIn folder. I check it to see if anything important is there, most of it is not important.
Facebook recently made a Facebook at Work site for employees to communicate with each other. I think it competes with LinkedIn.