Here's a brief but very good article from OSA's Optics & Photonics News (OPN) on the final servicing mission for the Hubble Space Telescope and what it's expected to accomplish in terms of HST's astronomical capabilities. STS-125 was scheduled to launch next week but was recently pushed back to February 2009 or later because of the recent failure of an important piece of HST's data communication equipment. Since this is the final mission, they decided to delay it so that a replacement part could be prepared, and so the astronauts can practice to add this additional task to their already full mission schedule.
I've written before about STS-125 and have even done some simulations of it with Orbiter (picture above). It's an important mission and worth waiting a little longer to make sure that HST will be ready to give us another five or more years of scientific results and beautiful images of our universe.