Thanks for writing this. I thought it might be a good idea to use the keystore that ADQ made with his first working app, "ktest":
-storepass password -keypass password -alias dktest/ditest/dntest
I've repackaged some of his files (K3 automatic key installer, jar signer script etc) and put them up at
http://kindlebru.com/devkeys.zip. These should probably be fine for signing apps in the near future.
The manifest line
Amazon-Cover-Image: logo.jpg will include a thumbnail (rel to the root of the jar archive). Thumbnails can be viewed by pressing the right donut button over the app. Full-colour jpeg and png images are supported, and are automatically scaled to approx 200x200 (official apps seem to use images closer to 500x500px).
For anybody else having trouble getting Kindlet jars off the device, I've also got them up at
http://kindlebru.com/libs.zip (had trouble telnetting, so I just created an updater script with the command "cp -r /opt/amazon/ebook/lib/* /mnt/us/lib").
The manifest of one of the official Active Content apps has the line
Network-Access-Grants: sponsored. Is this necessary to use 3G data?