Those of you old enough to remember when email starting rolling out to the masses may recall that many people preferred to just pick up the phone. Then they realized that email was a much cheaper way to contact people long distance. Or that it was nice to have a record of certain correspondence. Or that it was useful to send a message to multiple people at the same time. Or so many other things. Now most of us have situations in which email seems best and others when calling seems best. See also IM/Chat. See also phone text messages.
If you only use social media for a vague purpose (i.e. being “social”) using multiple sites can easily become overwhelming, but you can greatly improve your privacy and your sanity if you use multiple sites for distinct audiences and specific content.
The easiest example of specialization is LinkedIn because it has a self-defined purpose: professional networking. Ideally (and despite the ill-advised ability to tie it to your Twitterfeed) your LinkedIn profile should only contain information that you would feel comfortable discussing in a job interview. Standards of formality vary widely across professions, but your celebrity doppelganger or the urban dictionary definition of your name are probably not appropriate content for LinkedIn.
Other sites don’t have a universal purpose like LinkedIn. A focus may develop over time--like how MySpace became primarily a networking site for bands--but until then you can use Facebook, Twitter, Buzz, Wave and whatever else you may find in any way you’d like. I only suggest that you decide on a purpose for each site you use, and as my husband would say, don’t cross the streams.
For example, you may have one site that is your means of public interaction where you post for all the world to see and try to collect as many fans/followers as possible, then you have another site where you only communicate with people you know in real life. Perhaps you have another site that is locked down except for a few very close friends. Your site that’s public facing may be where you share interesting links and observations. Perhaps they have a theme, perhaps they don’t. You might then choose to keep your updates about your personal life somewhere else. And if you like to post complaints about your work, you'll want to restrict those to a site where you don't add your co-workers and boss.
Of course you may be an Internet exhibitionist who doesn’t care who knows all your personal updates (or you may want as many people as possible to see them). Then, I would argue you only need one site. Pick whichever one best fits your content and send everyone there.
Don’t try to fake activity on multiple sites by autofeeding content between them. Rather than strengthening your presence on all the sites this tends to dilute the meaning of all of them. Each site has its own strengths and weaknesses, which is why they each deserve their own content. Twitter has the advantage and limitation of brevity. Buzz has, for better or worse, the tie in with other Google account content. Facebook has…well…a whole lot of users. Sure you may sometimes want to share content in different places, but it’s best to do that by choice (such as the #fb tag for posting selected tweets to Facebook) rather than copying everything automatically. Twitter followers don’t want to see your truncated Facebook statuses, and Facebook/Buzz users don’t want to see Twit-specific garbles like, “lol RT @TwitGod @TwitDude Only if she’s paying #HashTagThatMeansNothingOutsideTwitter.”
I admit that a variable is your audience and what site(s) they use, but just because your friends are split amongst sites doesn’t mean you have to post everywhere. Someone who wants your content will find a way to get it. (For example, capturing your feed in an RSS reader.) And if they don’t…well, the world won’t end if someone misses your latest quip. Really.
So, will I use Buzz? I don’t know yet. If I do it will probably be for close friends only since it is linked to my email, something most of my Twitter followers, LinkedIn contacts and even Facebook friends don’t have. And I like it that way.
Should you use Buzz? Only if it gives you something new that is useful to you. Otherwise just scroll to the bottom of your Gmail screen and turn it off.