Fine, one day I will learn how to speak to human beings, up to now I can barely write …

Summing up, all PPAs will be associated to a new and unique GPG key created by Launchpad, it’s public part will be uploaded to the keyservers ‘web’. The only purpose of this key is to sign the repository contents, i.e, every time a change happens in a suite (packages get published or deleted) it will get re-signed. When `apt` operates on a signed repository it can authenticate the packages being transferred, only accepting signatures from known keys.

I hope it helps. Not that I think the ‘multiple-ppas’ topic was well explained, but that can wait.

Feel free to contact me on IRC (cprov at #launchpad on freenode.net) if you have any doubt.