It helps that I was "due" a large refund. Yes, I probably should have proactively reduced my withholding rate last year, but it was all so complicated. But between filing jointly with a lower earning spouse (last year, at least), buying a house and repairing a rental unit, I managed to work the angles substantially. Filing now, I get my substantial refund in a week or so, and I can put it to better use than as an interest-free loan.
Also learned a lot about what I should be doing financial and paperwork-wise with my little rental business. Encouraging, though -- on an AGI basis, we made 57% more in 2006 than 2005, but managed to reduce our effective tax rate. If I could just achieve 57% growth annually for a couple more years, I might actually make some real money...