Certainly I make 'estimated payments' but my estimates are often 'off' and seem to somehow be weighted heavily towards the end of the year.
Silly me, bad at math I guess =P.
I simply utilize this suggestion "If you expect your income to increase or to decrease significantly, you may want to calculate your estimated taxes using your projected total income.".
I guess i'm a pessimist, I always expect the rest of the year to go really badly and my projected total income tends to be lower than it actually is by the end of the year...Happens every year ;).