IRS Error in Your Favor

I got a letter from the IRS today, which started with this sentence:

We are writing to you because there is an error on your 2004 Federal Income Tax return.

Uh, oh. So I read on.

The amount entered for standard deduction was incorrect for the filing status claimed on your return.

The error was that I'd taken too small a standard deduction, and that they were thus increasing the size of my tax refund.

This is great news for me, but I wonder what percentage of returns "fixed" by the IRS end up reducing the tax payer's payment?

Anyway, I have to say I'm impressed. Maybe all that money the IRS spends on IT infrastructure is actually helping the little guy.