How long is the hubble telescope going to be used?

Since the Shuttle fleet has been retired, there's no longer any way (unless another one is developed) to service HST. Its last Servicing Mission was designed to keep it flying until at least 2015, but it's a safe bet they'll keep it flying as long as the gyros and the Fine Guidance Sensor are still operational. Once it's no longer operational, plans are to bring it down over the ocean in a controlled re-entry.

Hopefully the James Webb Space Telescope, HST's successor, will be ready for launch in 2015, but there's already been talk by the current administration of scrapping the budget, which would not only cost millions of dollars and man-hours wasted, but eliminate thousands of jobs as well.