For some combinations of virtualenvs, distributions, python version, and virtual environments, the macosx backend does not respond to key_press_events.

I can confirm failures with mpl 1.2.1, OSX 10.8.3, anaconda v1.4.6.
From the thread on matplotlib-users, Scott Lasley has failures with:
mpl 1.2.1/1.3.0r2, OSX 10.8, python3.3.2 (framework python.org in virutalenvs)
but
mpl 1.4.x not installed in a virtualenv works.

The following script ought to respond to key_press_events.

import pylab as plt
plt.switch_backend('macosx')
# plt.switch_backend('tkAgg')

def print_event(event):
    print event

fig = plt.figure()
fig.canvas.mpl_connect('key_press_event', print_event)
plt.show()

@mdboom edit: Adding "sprint" to the title, since I overheard a lot of work being done on this there.