I claimed 0 last year on my W4. According to my CPA, I still owe IRS $1,176. I don't get it?

Filling status: Married, filling separately
Total income: $51,667
State: California
Charitable contributions: $50
Update: My spouse took a standard deduction.
Update 2: 2010 Federal Income Tax Withholding: $5,200.01
Update 3: Thanks everyone for the insights! I'll start withholding extra $$$ from every paycheck.
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