Let's pool our thoughts: best practices for Salesforce ISV/OEM app development.
To help foster an ongoing conversation among Salesforce ISV and OEM partners (aka developers of Salesforce AppExchange apps) I started this discussion on the Salesforce ISV Partners LinkedIn group, which I encourage fellow ISV's/OEM's to join.
Leveraging these libraries is definitely a best practice, don't reinvent the wheel! As jQuery quips, "write less, do more!" As a Salesforce consultant, I think, this is generally the goal :).
This makes it very difficult to mash-up/integrate Visualforce Components or Pages from multiple ISVs into a single page. When faced with this, a common developer response is to stop using the latest version of the external library and trying to make their code work against the earlier version of the library forcibly included in the page (perhaps by a managed Visualforce Component or embedded Visualforce Page). Fortunately, there is a better way to avoid this.
So this namespace is just about the safest global variable you can use in the Salesforce world (anyone else who messes with it is being very, very naughty).
As a brief side-note, here's how to ensure that your app's "namespace global" has been defined before using it:
To protect your external library references, store a unique reference to these libraries within your namespace's object, e.g. immediately after loading in an external library, such as MustacheJS,
Then, even if some other VF Component or Page loads in a different version of this library later on, you will still have access to the version you loaded (0.7.2)