Other than facebook, of course.
I have written about how LinkedIn helped usget our first round of funding. It is one tool that i use everyday.

We use it for building our team, reaching out to partners/vendors, create visibility for our company, and most importantly, ref check.
Building our team: We have hired four senior level team members through LinkedIn. No fancy pro accounts and such. Just plain old cold emailing works. Or better, reaching out through an existing connection. You cant always get results but far better than getting a database search done on a job portal.
Reaching out to experts/partners/Vendors: There are incredible ways to find potential advisors, partners on Linkedin, discussion forums, regular updates from your connections, and top headlines from linkedin which is customised to your profile.
Create visibility: Our twitter feeds are linked to our linkedin accounts (and our twitter is linked to our website feeds). So any website update gets on to Linkedin and to all our professional connections. (I just heard that twitter is cutting off the link to LinkedIn, what a bummer)
Ref Check: Its incredibly hard to do good ref checks on a senior profile. Linkedin gives you their entire professional history, and if you are networked enough, there is some link you can find to the person. Isnt it better to get the reference from a person you know, rather than the candidate?
So, if you are arent leveraging LinkedIn, start today. Spend a few minutes everyday reviewing updates from your connections. Be proactive, do a search on a specific issue that you are dealing with, you will amazed at what you will find. E.g recently we launched Net Promoter Score tracking across our hospitals and I found that i had more than 10 connections that i could speak to who had expertise in NPS.
As with everything else, please dont take my word on everything. Try it yourself, an investment of 9 mins a day. Its the next best thing to shaking hands in person at conferences or going to the right business school.