Today astronauts completed a second EVA, this time repairing a gyroscope on ISS that has not worked properly since June, 2002. Gyros are used on ISS (and many other satellites) to maintain its orientation in space. The astronauts spent 7 hours, 14 minutes working, and the gyro is doing well now (despite an early glitch where a connector was not connected properly), according to NASA.
According to NASA engineers, they are not yet comfortable clearing Discovery for landing yet. There are two places where some "gap filler" material is sticking out between tiles, and it is feared that this material may disrupt the airflow around the belly of the orbiter on re-entry, causing extra heating on certain tiles "downstream" of the where the filler is sticking out, which may be more than those tiles are designed to handle. I've heard it said that the engineers want less than 1/4" of this gap filler to be exposed, though in at least one place, there is over an inch exposed. Flight administrators may call for this material to be trimmed down during the third EVA of this mission, though the issue is still being studied. In that case, one of the astronauts would work from the end of Shuttle Remote Manipulator Arm (CanadArm) and cut/file it away. The 3rd EVA is scheduled for Wednesday.
I am still awaiting word of the results of the analysis of the reinforced carbon-carbon on the leading edge of the wings of the orbiter. This information is expected later today or tomorrow.
A good link for following along with the progress of the mission and the status updates is SPACE.com's Return to Flight page.