Private accounting is the 4th most recession proof job out there. Think about the very function of the job. Accountants deal with the money. Ever heard of a "bean counter"? It is typically used as a derogatory term. However, when times get tough, bean counters become important because they can outline what the company can and can't do within the bounds of its performance.
Furthermore, if times are tough, some might be more willing to hire a CPA to prepare a tax return rather than using TurboTax. Perhaps the human element will be able to find more deductions, etc.
I do believe that the large firms (big 4) are laying people off in proportion to the amount of business they are losing due to clients liquidating or going with a cheaper firm, etc.
Nobody is 100% safe in any industry. Except maybe a Dr. But, I'd tend to say that that compared to being an auto dealer, real estate agent, construction worker, or an airline pilot, its probably one of the safer bets.