In my last projects the roll of social networks was fortunately really present. In the last 5 years you could see a constant growth of importance within this medium. Though i still have to kinda sell this topic to clients. How come?
I think one thing is that people really think more in topics rather than connecting them. But why not connect private fun with work. Especially then internet makes there no limitation.
So when creating a new site, lets say a portfolio, why not connect it with your favorite network? Most likely you will reach as many, rather more people, than with only your new site.
Nowadays social networks are so powerful and many people like to show their favorite artists or brands.
Why did Cola Cola reward 2 guys who created their fan page of the product? Simple because it grow so rapidly that they got a promotion worth at least 2 advertisement spots on TV during the best air time.
So while creating web pages it is worth to consider social network as an additional source or like a satellite site. Big ones are Facebook and Myspace of course, but also smaller ones can be worth a try if they cover a special target group. Another advantage of social networks can be also the offer of their services. For example gives you youtube a strong Video streaming function or have u ever consider the mobile version of your site on the net? Some networks offer a really easy access to this.
So networking, as i call it, is for sure worth a consideration and for me belongs to creating websites just as search engine optimizing and marketing.