I decided to buy some as it fell. In the fifteen seconds it took to press F5, enter bid (of $25 below prevailing price) and click OK, the price had fallen by $70. So I think for the first time ever I ended up paying less than my offer.

It ended up at $690, about 15-20 minutes ago I think. Now? It's $840 again. (My investment in bitcoin is turning out quite well, but I'm actually quite glad I didn't spend all that much in the first place.)