I've been using 2.3.0 for quite some time because it's the version Apple provides with OS X 10.3. This works out just fine most of the time, even though 2.3.3 is the latest version. However, it's definitely possible to hit a nasty stardard library bug or performance issue that has already been fixed.
For example, the _strptime module in 2.3.0 didn't cache locale settings. This misfeature makes it (in my experience) about 30 times slower than it should be (~20 dates/sec here); completely unacceptable.
Short of using PYTHONPATH (a total kludge, IMHO), it's not obvious how one would go about overriding (without overwriting) bits of the standard library; site-packages and any pth files are appended to sys.path long afterwards. Fortunately, someone already thought of this and placed an obscure feature into site.py: pth files can import arbitrary python code!
So now all you have to do is create a folder for standard library fixes, a python module to inject it into sys.path, and a pth file to make that happen whenever you start an interpreter. Here's mine:
Now create /Library/Python/2.3_FIXES and drop all the standard library updates you need right in there. I suggest fetching _strptime.py from 2.3.3 right away ;)