Can you learn YAML in five minutes? I did.
Then I read through a lot of the YAML articles, web, and spec this weekend. I was kind of aware of YAML some time ago, but this was my first in-depth look.
YAML appears to be just popular enough to have a future, but of course XML is a juggernaut.
I like that YAML maps to simple data structures found in essentially all modern languages. There is no separate "DOM". YAML also appears to have a good set of base data types with extensibility. On top of all this, the syntax is significantly simpler and more human readable, which also means it can be hand edited more readily.
YAML might make a good syntax for a build system, as opposed to ANT. It would also be a good candidate for "preference" files and other text documents that people read and write by hand, but also process with applications.
There is a simple mapping between YAML and a subset of XML. YAML is a good deal more compact than XML, although I wonder of that would significantly reduce the benefits of HTTP compression on large files. Depends on the markup to content ratio I guess.