Here is that in from 32- and 64-bit Python 2.6b1:

> ./python (32-bit)
Python 2.6b1 (r26b1:64398, Jun 20 2008, 09:20:49) [C] on sunos5
Type "help", "copyright", "credits" or "license" for more information.
>>> import math
>>> math.log(float('-inf'))
-inf
>>> math.log(float('inf'))
inf
>>> math.log(float('nan'))
nan

> ./python (64-bit)                  
Python 2.6b1 (r26b1:64398, Jun 19 2008, 20:27:39) [C] on sunos5
Type "help", "copyright", "credits" or "license" for more information.
>>> import math
>>> math.log(float('-inf'))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: math domain error
>>> math.log(float('inf'))         
inf
>>> math.log(float('nan'))
nan

Look like a Sun issue, doesn't it?