Adjusting exemptions question

[taratru]

I am a teacher and I recently quit an extra duty that was an extra 10% of my contract pay, which amounted to about $500/month before taxes. DH is also a teacher in the same district and his situation hasn't changed at all.

The last few years, we've enjoyed a pretty healthy refund in the spring, but I think it's a better idea to adjust our exemptions to have more take-home pay throughout the year, especially with my pay reduction.

I tried to muddle through the IRS calculator, but I really have no idea what my 2012 numbers will be. I used a simple one on Kiplinger's that told me I could claim 12 exemptions and still break even at tax time with an extra $524 take home each month. I don't think we should cut it that close.

I'm currently claiming 2 and DH is claiming 0. We have 3 kids.

So I suppose three questions:
Is this something that anyone has done?
Does anyone have a reliable (and easy) online tool to recommend walking me through this process?
Should I be the only one to change my exemptions to a higher number, or should we split them between us?