Using errorbar does not properly center the errorbar on the marker. See the following example and output. The issue persists in the legend as well. The errorbar is a few pixels off center and changing the linewidth does not solve the issue. snap kwarg has no effect either. I have reproduced this using matplotlib 1.2.1 and 1.3.1 on Mac OSX 10.8.4.

import matplotlib.pyplot as plt
plt.errorbar([1],[1],[0.1],fmt='k^',capsize=5,capthick=2,ms=9,markerfacecolor='none',mew=2)
plt.show()