Given that Linkedin has figured out how to run its application/web site on a "pay per use" grid (Joyent's accelerator service) they only need a handful of web developers and admins, and given the fact that their site/application's content is self-generating (you and I inputting our details) I dont see why they need more than a couple dozen staff doing non-sale/non-revenue generating activity.
Big valuation, significant risk-free revenues (I presume) and a list of staff short enough that even I could remember everyones name? Sounds like a great place to work!