I have just learned that the launch of the NASA/DOE Gamma Ray Large Area Space Telescope has been moved back a bit, to January 31, 2008. Prior to this, the launch was scheduled for December 14. Delays like this are fairly typical given how hard it is to get spacecraft hardware put together. Mission planners know there will be issues, but since they don't know what the issues will be exactly, they can't make an accurate schedule too far in advance. So as launch approaches, delays are inevitable.
I'll be glad to see this one go up. I worked on the education and public outreach for GLAST for six years, and I know it'll do amazing science.