I will use that as an exercise and a trading diary.
Based on the news that MtGox has a solution for the bug we can see that there is a bullish movement.
However, I think people is skeptical about Bitcoin and they didn't have confidence on it at the moment.
Based on this assumptions and knowing that in 671$ there is a resistance level I don't think that the bullish push will go beyond that. My entry point was shorting at 640$. I choose that entry point because I saw that volume was decreasing. I calculate my target at 86% using a Fibonacci retracement. I think that the low of this trend will be up the previous low and then stibilize between 600$ and 620$.