I gave Iron Python one more chance. I set out with a goal of getting the OpenID Python consumer example from JanRain up and running. The standard HTTPSocketServer failed to start. The socket file raised an exception when writing to the client.
After a lot of tracing, I found myself debugging the Iron Python file implementation. This is a deal killer for me. Iron Python has a lot of potential, but I have to decide if I want to work on Iron Python or build apps. Working on Iron Python would be a very interesting side project, and there are a lot of smart people working on it, but at this point I am more interested in Amazon's S3 and using OpenID for RESTful authentication, than I am fixing bugs in a language implementation.
So back to CPython it is. I should note, that even CPython doesn't provide totally transparent cross platform support. The file locking semantics prevented the OpenID consumer example from working on the Window's CPython implementation. I think this probably more of a bug in the OpenID code than CPython, but still the behavior was different.