'readline' module fails to build on OS X  in case of trunk and python 3.x. It have no issues with python 2.5 and 2.6 and python 2.7 alpha.

Here is the trace after running ./configure; make in trunk

Python build finished, but the necessary bits to build these modules were not found:
bsddb185           dl                 gdbm            
imageop            linuxaudiodev      ossaudiodev     
readline           spwd               sunaudiodev  

With that the uparrow-downarrow and other features fails which I suppose depends on 'readline'

07:31:51 l0nwlf-MBP:python-svn $ ./python.exe 
Python 2.7b1+ (trunk:79945M, Apr 11 2010, 07:14:54) 
[GCC 4.2.1 (Apple Inc. build 5646) (dot 1)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> t = 'test'      
>>> ^[[A^[[A^[[B^[[B

07:32:53 l0nwlf-MBP:CoreHD $ python3.2
Python 3.2a0 (py3k:79532, Apr  1 2010, 01:48:52) 
[GCC 4.2.1 (Apple Inc. build 5646) (dot 1)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import readline
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: No module named readline
>>> t = 'test'
>>> ^[[A^[[A

(pressing up-arrow for repeating the previous command fails)

However, an interesting observation is, 

07:34:00 l0nwlf-MBP:CoreHD $ python2.7
Python 2.7a4+ (trunk:78750, Mar  7 2010, 08:09:00) 
[GCC 4.2.1 (Apple Inc. build 5646) (dot 1)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import readline
>>> t = 'test'
>>> t = 'test'
 
No such issue here, 'uparrow' is working, thereby completing the previous command on interpretor. The version is python2.7 alpha as you can see. So I assume some recent changes broke something, it was fine earlier.