I think everyone who keeps saying that LinkedIn is evidence of a tech bubble should just stop complaining and take a short position. Put your money where your mouth is.
The underwriters who own shares from the IPO are not allowed to lend them out for short selling for 30 days. The institutional/retail investors who own shares can lend them out, but it is too soon for that to be enough volume to take any meaningful short position.
Of course, both your approach and mine make some assumptions about when the market will correct; mine assumes that it's further out and yours assumes that it's closer in, and timing that sort of thing is ridiculously difficult.