I've read this thread with great interest as I too got a letter. I don't know that this happened to everybody, but in my case, my mistake in the data entry was that I didn't add (in my head) the two amounts together. My wife and I both received a letter, so when TurboTax asked for the amount on the letter, I put in $1000, thinking that it would ask me again for the amount from my wife's letter. It clearly states (but I didn't read) that you should enter the "combined" amount from both letters in that field. So my CP11 said, hey, you shorted this by $1000...which I did. I too had to go check my tax return and see that I only put in $1000 when it should have been $2000. Live and learn. Thought i'd share.
Todd
