I've noticed that Icculus has been having problems lately with slow performance, images don't load half the time. I had figured that someone from one of the other hosted projects was pushing a big SVN update or something. Turns out the server hard drive was dying. Now it's completely down for repairs.
Ryan Gordon, who runs Icculus from which the GtkRadiant site is hosted is currently doing repairs. It'll be back up soon enough. Downloads are still being mirrored at RobotRenegade.
Edit: Everything back to normal.