In the "Post Build Action" section, under the "Build other projects" subsection,
there is a checkbox for triggering the downstream projects even if the build is
unstable.

An additional checkbox for triggering the downstream projects even if the build
fails would be useful. This would create the following XML in the config.xml:

<hudson.tasks.BuildTrigger>
<childProjects>ProjectName</childProjects>
<threshold>
<name>FAILURE</name>
<ordinal>2</ordinal>
<color>RED</color>
</threshold>
</hudson.tasks.BuildTrigger>

I've manually modified this XML in a config.xml file and the behavior of Hudson
is exactly what I've described above. Thus, all that's required is a single
checkbox to the interface for making the above XML changes.