There is an exception as mentioned there. If you pay an amount equal to 100% of the previous year's liability (110% if your AGI is over $150k), it doesn't matter how much more you owe in April.
(I personally ended up with a 2011 tax liability that was something like 160% of my 2010 liability, but I'd paid estimated taxes equal to my 2010 liabilities. So I had to cut the IRS a pretty big check in April, but had no penalties.)
(I personally ended up with a 2011 tax liability that was something like 160% of my 2010 liability, but I'd paid estimated taxes equal to my 2010 liabilities. So I had to cut the IRS a pretty big check in April, but had no penalties.)