Love them or hate them, review sites are here to stay. But don't take my word for it:
But you don't have to be Rich Barton to recognize how consumer review sites are changing the way we research products and services. Your potential clients expect to be able to find a variety of information about you online. One of the things that they expect to be able to find is what your clients have to say about you.
And Google knows this very well:

As you can see, Google SERPs are filled with reviews. And for local legal services searches, this trend is likely only to continue to increase. In fact, we will soon see reviews from people we are connected to in paid search results too.
Action Items
You certainly have the choice not to participate online. But you won't be able to keep yourself offline forever. The odds are stacked in favor of the fact that eventually someone will say something about you online.
A better course of action would be to take control of your listings on these sites. At a minimum, you can claim, update and optimize these profiles. Most of them are free and can be completed quite quickly. In fact, making sure that your information is updated, accurate and consistent across these sites will actually work to improve your visibility in local search results.
Your next choice will be to decide within which (if any) of these sites are worth paying for enhanced visibility.
Some lawyers on Google+ recently discussed whether or not to pay for advertising on Yelp.
First, it's important to keep in mind that it's impossible to say "x" works for everyone. I've seen various online lawyer advertising programs perform or fail for different firms based on all sorts of factors (i.e. type of practice, location, budget, etc).
Second, if you're considering whether or not to spend money on any of these programs, one of the things I recommend that you investigate is how well the platform appears in searches relevant to your practice.
Take the above "personal injury attorney seattle" search engine result page.
Avvo, Lawyers.com and Yelp all appear fairly prominently. Of course, the lions-share of clicks will go to the number result. Further, this is only one isolated search. You should research a variety of terms to analyze whether your ad will likely attract eyeballs, clicks and calls.
At the risk of stating the obvious, any advertising program you participate in should be ultimately measured by return on investment. Which means you need tools that will track impressions, clicks, inquiries, open files and fees.
Unfortunately, most lawyers don't have such tools in place and tend to measure their advertising with their "gut."
Which leads them to conclude, as John Wanamaker did:
"Half the money I spend on advertising is wasted; the trouble is I don't know which half."
Lawyers that complain that they don't have insights into the effectiveness of their online advertising really have no one to blame but themselves. The tools are available. And they're not very expensive.
All this said, starting any advertising program is inherently speculative. At least at the beginning. The good news is that now you can efficiently measure it and stop doing what isn't working so that you can do more of what is.