$250mil/year is 1/100th of what they eventually got acquired for. Linkedin was probably eventually making more than that, too (need to look) but I'd be surprised if revenue was the main reason for LI's success, probably more of a nice to have...
LinkedIn has constantly amazed me as far as how little they have done with their main asset, the professional social graph. That they don't offer paid products for hosted professional associations, or verified credentials, a CRM, or even intra-organization communication fascinates me. There are so many other examples of how you could make money with what they have, not even counting creepy ones.