Obviously it was an idea waiting to happen… This week, both Tribe and LinkedIn announced major new partnerships to include access to job listings to their users and help members network their way into the hiring managers.

Tribe will be partnering with CareerBuilder.com, giving Tribe users access to CareerBuilder’s 400,000 job postings. A launch date was not announced.

LinkedIn has partnered with DirectEmployers, offering networked connections into nearly 250,000 jobs. LinkedIn’s partnership is actually live, and I checked it out. It’s really simple, but very cool. You search for your job by keyword and location, and at the top of the job listing page, it gives you how many people are in your LinkedIn network at that company, how many of them are in the same city as the job you’re looking at, and a link to show them. Simple, but effective.

These announcements come hot on the heels of the launch of Monster’s new networking service. They also show a shift towards a viable revenue model for online social networking sites already proven by Craigslist.