This is actually a stress crack caused by the speaker. It's manufacture fault and HP is aware of it. They told me that the fixed or replaced unit will have the correction and " will not crack". My HP actually crack got larger every week even inside the box until it reached the screen and I could lift the piece and see inside. I am not confident that the next device will not crack so sadly have decided to sell and get another tablet (No Apple). I love webOS but I need memory slot as well as the capability to attach to a screen.
No cracks, been using it near enough every day since, carrying in a bag to work, on the bus etc. Bought in october after a lucky find in carphone warehouse (the last lot)
Got an Hp case on it, as long as it still works, if it gets a couple of cracks I'm not bothered- bit of gaffa tape and were off again.