It is very rare for me to experience a lock up on an Ubuntu machine. However when a program hangs for whatever reason and hogs all of the system resources it gets a bit frustrating. It would be nice to be able to kill the application quickly and move on with the work you were doing.
When a program hangs and you want to kill it, open a terminal and type xkill. This will turn the mouses cursor into a cross X. From here simply click on the window of the application that is hanging and viola… it disappears immediately minus the hourglass, blue screen or spinning beachball.