Ever selected 173 samples in Analyze! and hit "Raw Data" or "Analyze" and PFE takes off doing its thing, but then you realize you messed something up and need it to stop? In my experience the "Cancel" button in the lower corner doesn't actually cancel in this situation, and one is left waiting for it to finish.
My "tip/trick" is that you can go up and click "Pause Between Samples", and when it finishes whatever sample it's currently working on, it will pause and the "Next" button will light up. At this point, the "Cancel" button will now stop PFE in its tracks.