I'm researching how to best extend a C++ application with scripting capability, and I am looking at either Python or JavaScript.  User-defined scripts will need the ability to access the application's data model.  
Have any of you had experiences with embedding these scripting engines?  What are some potential pitfalls?
Lua is also a great candidate for embedding in programs. Its very self contained, and even the native cross-language call system isn't bad.
For JavaScript, your best bet right now is to look at V8 (from Google), which is easy enough to work with.
Embedding a scripting engine in C++