There's no need to mention the importance of a good network of contacts when it comes to looking for job opportunities. One of my student jobs I got through a friend (for his father's company), as he knew a bit about what I was doing as a part time job then, and they required someone to help them in that area.

Another job at SAP I got through my former flatmate. He did some Java programming there, and as he was going to Australia for an internship for a few months, they needed a replacement. I just came back from my internship in Singapore and was looking for a new student job, thus it was a perfect timing, and I took over from him.

These are cases where a network of people that I had close contact with in "real life" helped me. However, I also have two examples (my two most recent jobs) that show that it's also possible to find a job through one of the social networking websites. I'm sure that there are people who found a job through, for example, facebook or studiVZ, but the more important networks for these 'business-related' activities are LinkedIn and XING. LinkedIn has a lot more people on it, whereas the XING interface is a lot more usable in my opinion.

As for the job before my current one, I got it through XING. I contacted some people in Singapore through it, as I wanted to find an internship/thesis job here. One of the people I messaged replied saying that there might be an opportunity for me. As it turned out, I asked just at the right time, as they were looking for someone to help them with an IT project, and were considering hiring an intern for it.

As for my current job, which I started recently,  I was contacted by a headhunter through LinkedIn. As I always keep my profiles as much up-to-date as possible, the headhunter saw my SharePoint experience, and as it matched the requirements nearly 100%, he contacted me and asked if I was looking for a job (which I actually also was at that time).