Why AMF Rocks and beats XML
Ted made a great summary of why AMF is Flash's file format of choice.
http://www.onflex.org/ted/2007/11/abcs-of-amf.php
While I've touted the benefits about persistence and serialization of native classes in previous posts (see persistance or serialization categories). Often XML is preferred for data interchange with servers or text editor compatible configuration. Here Ted had a gem in the comments, comparing why using XML inside of AMF over XML in a text file, rocks!
E4X is super handy for querying the data and returning collections after parsing to xml. That said XML is a native object and can be included in AMF3. The data is stored as a string zlib compressed and when deserialized becomes an XML object again.
bytes.writeBytes( new XML('') );
This gives you zlib compression and benefits of e4x in one go. zlib is very effective on xml and can compress documents as much as 20X, I have seen 300Kb XML files become 7K given tag redundency in the ASCII text.
The XML human readable is important as often for games and such that I build, but frequently it's doesn't make sense to build a configurator given the many excellent XML editors out there. In addition it's very easy for most servers to generate, where they can't generate AMF as easily. But there are two compelling benefits to going that route:
1) As the XML grows, compressing things by up to 20x can improve the responsiveness of the application (like startup of a website), and reduce network costs.
2) XML stored this way is native data type to Flash not a string...meaning it's already an XML accessible to E4X instead of a random string that has to be parsed into XMLNodes. Reconstituting the data out of the AMF stream still takes overhead, but it should be much faster than parsing it from interpreting tags and attributes from the plain text, as most the marshalling code is in C inside the player instead of actionscript. Read better experience for end users.
What occurs to me now is that either a very simple AIR app act in a similar fashion to Winzip for compressing/decompressing text for consumption by flash, or act as a simple text editor, just using a text field.
I'm sure that Adobe will open up the AMF API so that servers can generate raw AMF without using remoting or RMTP. This will open up the possibilities for CMS driven websites to prerender sites daily out of database requests.