OK, there is a lot of misinformation in this thread about the CPA Exam so let me clear up a couple of things.
CPA is not a designation - it is a state issued license. If you are a CPA, that means you are Certified (licensed) to practice in that state as a Public Accountant. Only a licensed CPA can sign the audit opinion on the financial statements of a public company.
Passing the standardized CPA examination is required for licensure in all 50 states.
Each state has its own requirements (in addition to the exam) for licensure, such as work experience, education, etc.
This link probably has more information than anyone would need:
http://www.aicpa.org/MediaCenter/FAQs.htm#cpa_answer7