Message updated by Figment! on 02-03-2009 at 7:55 AM:

The Walt Disney World Resort has internally announced tentative completion dates for the Space Mountain and Tommorowland Transit Authority Refurbishments. Currently, the Tommorowland Transit Authority is scheduled to re-open August 19, 2009 and Space Mountain is schedule to re-open November 22, 2009. Both attractions are still scheduled to close April 19, 2009.
Message updated by Figment! on 02-02-2009 at 3:55 PM:

The Walt Disney World Resort has announced a tentative time period for the refurbishment to its Passholders in their most recent newsletter.

Quote Originally Posted by Mickey Monitor: Official Passholder Newsletter

In 1975, we were lucky enough to become home to the original Space Mountain® attraction. And now we’re returning the favor—by
returning the attraction to its “opening day” splendor. Beginning in
April 2009, Imagineers will perform a “space-lift” to make this classic
even better.

Don’t worry. The original elements—from the serpentine track to
the exterior silhouette—will remain unchanged when it reopens later
this year.
Message updated by Figment! on 01-06-2009 at 10:09 PM:

In addition to the internal announcements, the Walt Disney World resort has now publicly announced that both Space Mountain and the Tommorowland Transit Authority will be closed for refurbishment April 19, 2009 through at least July 31, 2009.

It should not be expected (at this time) that the attraction will re-open August 1, 2009 rather the current public refurbishment calenders only run through July 31, 2009.

Message originally posted by WDWRox on 01-05-2009 at 12:09 PM:

I found this information on another site, and it sounds pretty definite about the time frame for the big refurb of Space Mountain:

"Space Mountain is set to begin it's year long refurbishment on April 19, 2009. It is expected to open late 2009 with no specific date."