I did have taxes withheld - I only claimed 1 on my W4 - but I made about $10k more in total taxable income than I did last year.
I also had about $7k in "capital gains distributions" from leftover college fund money. But I know next to nothing about that account, it was set up by my parents when I was a kid, is completely managed by my Morgan-Stanley guy and I didn't make any withdrawals or recieve any income/dividends from it in 2006, but as soon as I put in that $7k number my taxes went from getting money back to owing $1500.