Looked at a flight to Greece a few months ago and put a price watch on it. When I first looked at it, it was £50. Ultimately decided not to go - but never got rid of the price watch as it was fascinating watching it fluctuate. It did go down to £20, then up to £300, back to £75 and not it's fluctuatiing between £150 and £205. The flight is about 2/3 full at the moment.
I would just love an insight into their algorithm. Are they playing a game of poker with people? I notice that sometimes the flight has gone down and then the next day, it's back up again.
The price watch email is a great tool though.