I've done basically exactly the same thing. Much of the webapp is written in python, but the core performance critical part is written in C++. There basically wouldn't be any other way to make that particular app work, and this approach worked really well.
That being said, I never felt particularly inclined to write the whole things in C++.
> That being said, I never felt particularly inclined to write the whole things in C++.
Agreed, however one of the problems we are encountering is passing messages efficiently between RoR and the C++ components. Currently using XML until another method that is more efficient, but no less flexible, presents itself.
Personally I think the debate should be less focused on which language to write your web application in, and more on improving the glue between different languages so in developing web applications we can have the best of all possible worlds.
That being said, I never felt particularly inclined to write the whole things in C++.