As nasaspaceflight.com reports, Discovery has probably been hit by an object this morning. It is still unclear what the object was. Candidates are micrometeoroids or orbital debris, but it may also be a false alarm. The sensor reading, however, tells that the hit was tripple the previous max hit.
It is far too early to draw any conclusion. NASA is currently evaluating the issue. A final decision will probably be postponed until the end of the mission. Then, the heat shield is inspected with the so-called orbital boom sensor system (OBSS), which can detect damage. The late inspection is done since some flights now and it is especially targeted towards detecting on-orbit damage. So it is perfectly valid to wait for it.
Let’s hope this is no real incident. So far we had a flawless mission and I hope it remains that way ;)