Rotating axes label text in 3D

As a workaround, you could set the direction of the z-label manually by:

ax.zaxis.set_rotate_label(False)  # disable automatic rotation
ax.set_zlabel('label text', rotation=90)

Please note that the direction of your z-label also depends on your viewpoint, e.g:

import matplotlib.pyplot as plt
from mpl_toolkits.mplot3d import Axes3D

fg = plt.figure(1); fg.clf()
axx = [fg.add_subplot(4,1,1+i, projection='3d') for i in range(4)]
for ax,azel in zip(axx, [(115,10), (115,-10), (-115,10), (-115,-10)]):
    ax.set_title(u"Azim, elev = {}°, {}°".format(*azel))
    ax.set_zlabel('label text')
    ax.azim, ax.elev = azel

fg.canvas.draw()
plt.show()

gives

Update: It is also possible, to adjust the z-label direction of a plot, which is already drawn (but not beforehand). This is the adjusted version to modify the labels:

import matplotlib.pyplot as plt
from mpl_toolkits.mplot3d import Axes3D

fg = plt.figure(1); fg.clf()
axx = [fg.add_subplot(4,1,1+i, projection='3d') for i in range(4)]
for ax,azel in zip(axx, [(115,10), (115,-10), (-115,10), (-115,-10)]):
    ax.set_title(u"Azim, elev = {}°, {}°".format(*azel))
    ax.set_zlabel('label text')
    ax.azim, ax.elev = azel
fg.canvas.draw()  # the angles of the text are calculated here

# Read drawn z-label rotations and switch them if needed
for ax in axx:
   ax.zaxis.set_rotate_label(False)
   a = ax.zaxis.label.get_rotation()
   if a<180:
       a += 180
   ax.zaxis.label.set_rotation(a)
   a = ax.zaxis.label.get_rotation() # put the actual angle in the z-label
   ax.set_zlabel(u'z-rot = {:.1f}°'.format(a))
fg.canvas.draw()

plt.show()