What is the procedure for resolving Ubuntu lock-ups?
After the timeout and associated screen lock, wake-up activity such as mouse movement or key presses -- I usually use the harmless shift key -- fail to bring up the OS login prompt. Sometimes the desktop wallpaper will be displayed; sometimes the screen will be black. In either case, the cursor is visible and movable but hovering it on the left to get a Launcher bar will not result in a Launcher bar being displayed and hovering it in the upper right corner will not result in a drop down menu being displayed.
This has been observed on 12.04 with updates to early October 2013. Hardware: Samsung RF711 S04HK with Nvidia Optimus 540M.