If anybody is interested, I've written a cache loader for Amazon's S3. Just an experiment on my side and haven't spent much time playing with it, but it does pass CacheLoaderTestsBase.
If anybody wants the source, send me a PM. It's nothing fabulous and is liberrally ripped from the S3 sample code and the JDBCCacheLoader, but it seems functionally complete.
Could be an interesting CacheLoader to include in the distribution.
It could be an interesting addition - perhaps a bit too niche for the general distribution, but I would say start a wiki page on it, attach your cache loader there, and link the wiki page to http://wiki.jboss.org/wiki/Wiki.jsp?page=JBossCache