Tiny Speck has announced that Glitch will be permanently shutting down on December 9th, with forums available through the end of 2012. According to the official post, Glitch did not attract a large enough audience to become financially viable thus leading to the closure.
Unfortunately, Glitch has not attracted an audience large enough to sustain itself and based on a long period of experimentation and our best estimates, it seems unlikely that it ever would. And, given the prevailing technological trends — the movement towards mobile and especially the continued decline of the Flash platform on which Glitch was built — it was unlikely to do so before its time was up. Glitch was very ambitious and pushed the limits of what could be done in a browser-based game ... and then those limits pushed back.
Read the full announcement and the FAQ on the Glitch site.