The comments here are hilarious, they really reveal the IT bubble. The only real complaint about this purchase would be that LinkedIn was overvalued. And I wouldn't bet on that since Microsoft surely sent a big team of their brightest cookies to make a valuation of the company. But other than that, LinkedIn fits: it is a corporate social network, if you will. I know that "corporate social network" is almost an oxymor…
But in most other lines of work, the recruiters don't knock so often (or so cluelessly) ... and the access to other people's profiles actually is quite handy. Sales. Finance. Media. Education. Law. Non-profits. It's a long list.
It's anyone's guess whether Microsoft can execute the bulk of its strategic plan for LinkedIn. But the plan is not foolish.