Ah, that is most assuredly the question. I hear it all the time from authors on my writing lists who look at social networking as a necessary evil to separate themselves from the pack of authors, all crying for attention.
Most nonwriters think of social networking as an extension of their social life. Some view it as an online party. Writers see it differently though many do enjoy the social aspect of it.
Does it do any good in promoting you or your books or to increase name recognition? Most internet gurus and marketing experts give qualified answers.
"No, it won't sell books or increase name recognition, but it can't hurt." Or, "Yes, but only if combined with other efforts."
You see, the problem is governed by an immutable law of marketing: a consumer must see or hear a name approximately 9 times before it makes an impression. If you translate that into an individual viewing your web presence 9 times, you realize that the real problem is driving traffic (unknown visitors) to your social network page or website to view you and what you have to say.
If you're already famous or a rising star, that's probably pretty easy. If you're starting from ground zero, how do you get those numbers to sign up to follow you or be your friend?
Chasing Your Tail
You can spend endless hours tweeting or friending it or whatever you think might work, but the honest answer is that no one knows. I suspect a lot of people on the social network sites get ego strokes from accumulating friends and having innumerable strangers sign their walls or whatever.
I conducted a little survey last year on a promotion loop I'm on. I asked everyone to tell me what social network they used and if they thought it helped. Not one single writer could honestly say they thought their efforts were worthwhile yet they felt compelled to continue because everyone did it.
That's a trap. We each have only 24 hours a day to work at our career, take care of domestic stuff and our financial/clerical responsibilities, and to achieve that important task of having a life. If you're feeling overwhelmed and burned out, maybe you need to assess how you're spending your allotted time.
Time is more valuable than money because you can make more money, but you can't make more time. Spend wisely.