The most likely answer to your question regarding what the 'market expects' is perhaps that the market expects that currently Linked-In like a lot of other startups has been plunging almost eveything it makes into building the business and brand. So right now the net profits are pretty low percentage of income (roughly 1.5% of revenue)
Given the size of the other numbers, it doesn't take a lot of movement in the right direction to get a big change in that tiny final number.
The other factor is the gap between their Net and the Income Available.. I think (but I'm making a logical guess here) a large part of that gap was paying off the losses of the prior two years. If that's the case, and everything else is static, then next year's 'available' number ought to at least triple.
In order to grow the net, all LI needs is to either continue current trends of growth in expenses relative to costs, keep expenses steady and experience a slight growth in income, or find a way to reduce expenses without having it impact income. Or something in between those three. If we take the first case as an example, income has been roughly doubling every year, but expenses growing less than that. if they were to continue that, but manage to get some economy of scale and have expenses grow at a slower rate, then the jump in net income ought to be substantial.
most of the trends you could project end up with a big growth in the bottom line.. but yeah I gotta admit, none of that gets you 117X growth in a single year. So the conclusion I would draw is that the market is trending a few years out and being pretty optimistic given the current PE ratio. Of course you could also conclude that the market is 'social network happy' and LNKD represents one of the few opportunities for the average investor to get in on that given that facebook and myspace are not trading on the open market