Much of what is seen in textbooks today came from images captured by the Hubble telescope.
The problem with making repairs is that any mission to the Hubble Telescope, makes it impossible for the Space Shuttle to reach the International Space Station in case of an emergency. This puts the crew and the shuttle at risk.
There could be a possible mission to fix the telescope in 2008. The fixes would extend the life of the aging telescope by approximately five years.
To top it off, the space shuttle will be retired in 2010, so this would be the last opportunity to take the space shuttle to Hubble.