Since November 29, the options lot changed from 1 BTC to 0.1 BTC, this means calls are akin to buying 0.1 BTC and puts akin to selling 0.1BTC. The naming was not changed:

O.USD.<Call or Put><strike><This or Next month>

but the strike applies to 0.1BTC. So, for example O.USD.C110T is a call struck at 1100 USD/BTC, expires last Friday of this month.

Note: In following formulas the strike number is used unmodified, for example with O.USD.C065T use 65 as strike.

How to calculate profit/loss?

BTCUSD - current 24h weighted USD price from bitcoincharts

Calls
Profits if price rises above strike, otherwise exercises worthless.
Profit on exercise in BTC: ((BTCUSD/10)-strike)/BTCUSD
Break even BTCUSD point: 10*strike/(1-buyprice*10)

Puts
Profits if price gets below the strike, otherwise exercises worthless.
Profit on exercise in BTC: (strike-(BTCUSD/10))/BTCUSD
Break even BTCUSD point: 10*strike/(1+buyprice*10)

Expiry
Last Friday in the month, midnight UTC are all *T options exercised automatically according to then current BTCUSD. All *N options are renamed to *T options and new *N options are created.

Going short
MPEx enables two ways to create options, which you can then sell short:

MKOPT - creates options of one mpsic, needs collateral:

• Each CALL requires 0.1 BTC of collateral irrespective of strike.
• Each PUT requires an amount of collateral equal to strike*10 / spot BTCUSD  + some MPEx-proprietary padding.

There is 2% fee.

SPLIT - creates CALL-PUT pairs at given strike. The given BTC amount is divided in half, one half used as collateral for calls and other one for puts according to same rules as MKOPT. There is no fee.

On expiry, unused collateral is automatically returned. At the moment, CoinBr does MKOPT/SPLIT manually on e-mail demand without additional fee.

You can exercise all options yourself at any time, make sure to check prices offered on MPEx first if it isn't better to sell the options. If the order book on mpex.co is empty, wait a few minutes. If still nothing appears, it probably can't get price data, you can come bitching about it to #bitcoin-assets. You are also free to offer any options you have for sale at any price, or place a bid instead of buying from bot.