It happens sometimes, but I've managed to restore the Nautilus without rebooting the system.But today, when I attached a file .svg by e-mail, he first caught the Google Chrome and then Firefox 5, and when I open the folder in Nautilus Ubuntu crashed. Making me to restart the PC via Alt + SysRq + B. I know there is a bug related to it, and I also know that there is no preview thumbnails for Nautilus, but that could be set up so only thumbnails of files .svg did not appear?