if you intend visiting usa -homeland security , page-28

Now all of the times I used to visit the USA over the years, they took the card out of the passport. In fact usually the airline check-in person would take it.

In the last three years, they didn't bother. But when they check your passport, their computer should be recording that you have left, thats why they don't seem to bother taking the card.

The last three times I was there, they didn't take it. I haven't had any issues from them thinking I was still there.

Next time I will follow your advice and make sure they take the card.