window.name as a data transport: a valid approach?

window.name isn't particularly good as a transport, as (AFAIK) it doesn't fire any events when it's changed. As a result, an application which was trying to use window.name as a two-way communications channel would have to poll it for updates.

As far as sites that actually use it: I've never heard of any. There might be some, but I've only heard this technique discussed in a purely theoretical sense.

More to the point, can anyone give me a solid reason why I shouldn't use winow.name as a data transport?

While window.name can be a true saviour when it comes to transporting data accross domain changes, the reason it cannot be used as real universal data transport mechanism is due to the lack of an api to store and retrieve data. For example localStorage provides setItem, getItem. Such an api is necessary to abstract from how values are actually stored and to prevent format clashes (which would arise if different libraries running on your side would store in different formats).

As far as I can tell, window.name has not caught on as a data transport. I wonder if my perception is accurate (thus the original question) and if so, I wonder why this is the case.

Since window.name does not provide such a store/retrieve abstraction layer – as described in my point above – 3rd-party librabries cannot know which format to use when storing data in window.main and hence will never use window.main as it is unreliable. If you (i.e. your main program) were the only one reading from or writing to window.name you could decide to store data in json format and store/retrieve accordingly. But what if a 3rd-party library also wanted to store/retrieve something and it decided not to use json and instead go with another of the numerous serialization formats... this would accidentally break your json format and definitely cause trouble.