The Python-in-the-page concept for Mix's Gestalt is great -- but as a beta still has some rough spots. This is the result of some initial playing...
Recompressing the .xap file at high compression will get you around ~25% reduction in size (for the python .xap, at least). The extra 5k saving for minifying the loader script is small change by comparison.
External script files (<script type="text/python" src="script.py"></script>) appear to be not (yet?) supported -- I get an unhandled error when I split the python code for the 02_python.html sample out.
Invoke() style needed to call into DOM properties is a bit tedious (as seen in the canvas sample).
There do appear to be some subtle interactions with existing scripts -- adding a hello-world button into an existing page with scripts+canvas+... silently did nothing for me -- I've not yet stripped this down to a simple problem case, but do be wary of this.