Pros of certification:
Job marketability for "desirable" employed positions ie. Rehabs, academic hospitals, certain private practices.
If you want to start climbing the chain of command you pretty much need to be board certified. ie. chief, medical director.
Lifelong learning. If you enjoy the field its a good way to stay engaged with the latest developments if you're not the type to study on your own.
Cons of not being certified:
"what? You're not board certified?"
Not meeting the minimum standard as established and promoted by the medical community. And by medical community I mean the doctors who pay to get certified-- even the ones who complain like the author of this article in psychiatric times.
Less money. The reality is that board certification pays. You pay the board with your time and money and the board pays you back with an even higher salary from an employer or insurance company. That's a lot of power.
Forgetting the material.
If you wait past 7 years you lose board eligibility and need to go back to your training program for mock interview tests and complete additional CME. How embarrassing!
If you're starting a family, moving, or undergoing a big transition after residency and plan on taking the boards I highly recommend delaying them and taking advantage of that 7 year window period. Look at it from the perspective of your psychological benefit. Just make sure you think you can pass the test the longer you wait.
If you don't agree with the boards then make a stand and don't take them. As TP mentioned, the job market is pretty good and this will likely continue to be the case for years to come.