[magician]

If you are in extremis, and nothing else is working for you, you can always use the Hail Mary key stroke: command-control-power key. This will execute a hot-reboot.

It is not ideal to do this, as it can occasionally result in a Mac that will not boot. If this happens, boot off your system DVD (hold down the C key on restart) and run Disk First Aid from the DVD as described above.

In my experience, the pinwheel of death is most often caused by an application or a drive which is not responding. The system is just stuck waiting.

Force quitting guilty applications is fine under OSX, as it is very rare that other apps will be affected. They run in their own protected memory space. Usually, you can simply restart the application, and resume working.

If you have a drive which is not responding, it will generally be because the cable connector wiggled loose. Just reseat it.

Hope that helps.