Tax filing help, which is more beneficial?

I got married october of 2010. My wife and I did not change or status on our tax deductions from our pay checks as of now. I was fiddling around with the deductions and found that if I changed the status to married, I would receive around 400 more each month. Can you tell me the benefits of married filing jointly, and married filing separately? I want to change the status on my paycheck, but will I need to pay more at the end of the year? Thanks in advance.