I'm not sure I agree with your Y-axis. It's labeled as % change, but doesn't really represent that. I would think what you have labeled as 100% should be 0% change, with positive and negative numbers instead of > 100 and < 100. At the very least, the label should be changed to accurately describe what you are representing.
Negative numbers pose a problem because they can carry ambuigity, and don't reflect symmetry very well. I changed the label to "% of 2011" for the bubble watch chart. I think I'm going to scrap the mean too, because it isn't a long-range indicator anymore. Here's yesterday's chart:
Chart by Dree12, Mt. Gox USD Open data from Bitcoin Charts
Left y-axis (100%): no change from 365 days ago; Right y-axis: price in USD
Black line: 2012, Grey line: 2011
Desaturated yellow: beginning of a month
Bright green/red: record increase/decrease