A lot of it also depends on how stable your income is. If you have wide swings, it's a little harder to gauge.
Last year we paid a substantial amount. I had a large capital gain in '08 that was unexpected, and had to cough up some money.
Then my wife and I both took early retirement offers, and our income for '09 dropped considerably. As a result, we have a good refund coming this year.
So for two years, I blew what I had estimated our liability to be.
Hopefully this year I can hit it closer so I don't have either a big payment or a big refund due. But the wife is making noise about going back to work, so who knows?
