Namespaces best practices

I'd like to get some feedback on a past topic that never seems to get resolved: Namespaces best practices.  The 3 options out there seem to be:

(1) Homogeneous Namespaces across applications.
 - All XML schemas use the same namespaces, and the developers make sure to avoid collisions

(2) Heterogeneous Namespaces across applications.
 - All XML schemas use different namespaces, and the developers have to do manage reading / writing / XSLT to different systems

(3) Chameleon / Proxy namespaces.
 - All applications maintain one external namespace, and use proxies or chameleon methods to have many internal XML namespaces.

I would love to hear developers / architect's feedback on how scaleable these different methods are, how easy it is to reuse XML Schema assets, and how manageable the namespaces are.

Thanks
Zach Friedland