I've never gotten certified, but that's only because it won't change my business a bit. No one has ever asked me if I'm certified. Most people if you ask them, What is an Arborist? they probably don't even know.
I enjoy actively studying for the exam and should probably take it some day.
Getting certified comes after becoming an ISA member. Then becoming a member of the ISA state or territory charter. You get educational materials sent as a result of your membership and are invited to be part of the state and international meetings and conferences. You have a pipeline to the current research and goings-on in our industry at levels other than your own, e-mail links and magazines to further your learning. In other words, even a solo cat can become part of the industry in a more connected manner by being included in something much bigger than himself (or herself!)
I've recently learned this, what the benefits of ISA membership are, and what's to gain from my Indiana charter membership. Between those two, and my TCIA membership, I get a lot of printed material every month to read. In addition to walking around the halls of Arboristsite and going out and practicing treecare every working day, it's pretty much total immersion.
In a way, I do feel like after 14 years of full-time practice as a treeguy, I probably shoulda gotten my
Certified Arborist by now. But I'm lame, I have only shallow excuses on why I haven't.
Here's a PDF for an actual Arborist Association Annual Conference:
http://www.indiana-arborist.org/Temp/2007AnnualConf.pdf