I'll be the first to admit - I'm a bit late to the Google+ bandwagon. I signed up six months after everyone else. When I got there a couple years ago, it was a post-hype empty room. And though Google claims to now have over four hundred million users, at least a quarter of which are active each month, GigaOm points out that the number is likely a bit inflated.
The same goes for Twitter. One hundred and forty characters is cool for scanning the mutterings of celebs, reading headlines from local papers, and being confused by surprisingly insightful spam bots. But are clients going to choose you solely based on clever tweets? Probably not.
I'm now on both. Religiously. I tweet every blog post. I retweet others' stories. I hang out in Google+ discussion groups (or "Communities"), especially Cloud Computing for Lawyers. They've both become useful tools, but not for direct client interaction. (Though you may be able to troll topical discussion groups, like surviving divorce.)
Don't get me wrong - blogs, tweeting, and other forms of online interaction can lead directly to clients. I've had more than a few readers contact me about their cases -- which I've turned down (not licensed in Alaska - sorry bro).
But the other place where these services can truly help is with professional development. Become a voice in the legal community and people will turn to you for advice and assistance. If you have a unique practice area, make that known to others. Social networking is networking without the booze (though, what happens behind the monitor ...), dress shoes, and social awkwardness.
I've written and tweeted about parental liability for children's' tortious acts. A potential client somehow dug up my personal email. I've written about small firm management and had former classmates call me for more tips after reading a few posts. I even had a lawyer write a long, passionate disagreement with my assessment of the effect of the "code of silence" verdict in a Chicago Police misconduct case.
To maximize your use of these services, and blogging, there are a few things to keep in mind. First, you have to be active. This might mean setting aside thirty minutes per day to check your social media accounts. Second, you have to be professional -- tweeting #gettnslizzard isn't going to impress anyone.
Finally, make your expertise known. If you are well-versed in fighting California's new DUI ignition interlock pilot program, blog like crazy about it. Contribute to legal discussion groups, tweet your posts or thoughts, and people will begin to recognize you as an authority on the topic. When they have a particularly difficult case, or a case outside of their practice area, they'll often ask for your advice, or pass you a client.