At least in Python 2.5 and 2.6 (I haven't checked newer versions), the 
PyDateTime_IMPORT() macro passes string literals to a function that
takes non-const char* parameters:

#define PyDateTime_IMPORT \
        PyDateTimeAPI = (PyDateTime_CAPI*) PyCObject_Import("datetime", \
                                                            "datetime_CAPI")

This makes it impossible to build code with warnings as errors, when
using that macro.

changing the definition to (const char *) seems like the right thing to do - a quick grep of the Python source and a search on google codesearch only shows uses with either string literals or string literals cast to (char *) in order to silence a warning.  I tried changing it on the 2.x trunk and it compiles with no warnings.

+1, any other opinions?

PyCObject is deprecated in 2.7 and removed in 3.x.  PyCapsule_Import() should be used instead of PyCObject_Import() and it already has correct signature:

Include/pycapsule.h:PyAPI_FUNC(void *) PyCapsule_Import(const char *name, int no_block);

Since this is not a bug, I don't think it is appropriate to change it in 2.x.