...the rest of the fleet has been grounded, as will Discovery when she returns safely to Earth.
According to this article, because the external fuel tank on Discovery lost a section of foam, NASA has decided to ground the fleet. This grounding is supposed to be temporary, until they can figure out a way to ensure that foam can't fall off of the external tank. As is widely known, the shuttle Columbia was struck by a piece of foam from the liquid fuel tank on launch, which caused catostrophic damage to a section of the heat shield tiles, manifesting upon Columbia's re-entry. After the Columbia disaster, the fleet was grounded for two and a half years, and a large amount of money and time was dedicated to solving the "foam problem," making sure that foam couldn't fall off of the external tank again. Even though the foam in the case of Discovery appears not to have impacted the orbiter in any way, it still shows that the foam problem hasn't been completely rectified, and thus the cause for the fleet's grounding.
I, and a few of my aerospace engineer friends, see this as more or less a sign of the end of the shuttle program as we know it. Having spent so much time and money "solving" a problem and finding that the problem wasn't solved (and in fact may not be solvable), we expect the next focus of NASA's efforts to be more towards the design and build of a next-generation vehicle than to the repair and upgrades of the shuttle fleet. While this means it's an interesting time to be involved in the aerospace industry, it also means that we will likely see quite a bit of time between now and the next U.S. manned space mission--after all, we will need enough time to design said vehicle and then get it qualified for space, which is a time-consuming task.
What does this mean for the near-term goals of NASA with regards to manned spaceflight?
*More dependence on the Russian Soyuz capsules for ISS maintenance and supply trips.
*Probable abandonment of the Hubble Space Telescope--NASA is reasonably convinced in part due to a study by the NSF (National Science Foundation) that robotic servicing of HST is not possible. While I disagree, I would expect them to abandon hope of repairing it in lieu of planning a robotic servicing mission. Of course, if they DO plan a robotic servicing mission, I think my thesis will play an important role in the design of the robot's hands and tools.
*Vechicle design may place more emphasis on a capsule-style (Mercury, Gemini, Apollo) vehicle, which has been more reliable in the past.
Again, more updates on the Discovery itself as mission landmarks occur. It will be interesting to follow what happens with the entire fleet, too.
UPDATE!!! The BBC has a much more satisfactory article about the grounding of the shuttle fleet. Find it here.