How awful is Facebook doing compared to LinkedIn? To find out, compare the two companies' year to year growth. As the following graph illustrates, LinkedIn is far surpassing Facebook on nearly every significant metric:
To be fair, some of Facebook's 2012 drop in profitability was connected to the company's purchase of Instagram, which is an investment that still might pay off. Even so, Facebook's underperformance in revenue and user growth is pretty hard to ignore.
Why is LinkedIn doing so much better? In my humble opinion, it comes down to business fundamentals. LinkedIn has a better business model, is less vulnerable to competition, and has better (i.e. smarter and more mature) management.