Google's App Engine sounds like a great way to deploy highly scalable web applications. Initially, however, you can only use Python to develop the applications.

One current limitation is a requirement that applications be written in Python, a popular scripting language for building modern web apps (Ruby and PHP are among others widely used). Google says that Python is just the first supported language, and that the entire infrastructure is designed to be language neutral. Google’s initial focus on Python makes sense because they use Python internally as their scripting language (and they hired Python creator Guido van Rossum in 2005).

Google Jumps Head First Into Web Services With Google App Engine

It will be interesting to see if Google does allow App Engine to use PHP or Ruby. I'm not sure but I would guess that both are more widely used for web applications than Python.