I was having some issues connecting to (although not pinging) python.org and some of the python-subdomains: notably the CheeseShop (http://pypi.python.org).
I disabled IPv6, and they all cleared up.
I don’t know if this was an issue with Internode’s IPv6 stuff, but it was being handled by my Airport Extreme. My iPhone was working fine, because it doesn’t use IPv6.
What a relief.
I had tried everything I could think of: from changing my DNS server, DHCP server, I even tried a reinstall of my OS (although this wasn’t why I did that - I wanted a cleanup of my dev machine).