I am using the MacOS X backend, and when plotting and saving a file, the dpi= option seems to be ignored:

fig = plt.figure()
ax = fig.add_subplot(1,1,1)
fig.savefig('test.tif', dpi=1000)

produces a file that has dpi=72. Is this normal, or is it a bug? If it is normal that dpi doesn't have any effect, it might be worth adding a warning so the user knowns the dpi option will be ignored.