Where I work, you don't have to wait till open enrollment to change withholding. You could probably march down to HR with your w-4 tomorrow if you felt like it.
Of course, my financial planner is recommending that we take extra out .... damned marriage penalty + living in a freaking expensive state + having the drive to succeed. If we were single and living in sin, we would pay less taxes and have a hell of a return this year, my wife would probably get an even bigger return as a "single mother".
damn government grumble grumble time for another tea party