There is some bug in the order book chart:
http://bitcoinity.org/markets/btce/USDIf I click the minus sign, the vertical scale goes from 0-100 to 0-15, when it should go to a larger scale. See images, before:
A similar problem also showed a month (or two) ago on the EUR-chart of mtgox, and then even on the US$-chart.
Either, this problem shows up and goes away all by itself, or it needs to be fixed for each chart individually...
PS: on mtgox/EUR the problem didn't show up again, yet, since back when it was reported in this thread.