Any way to retrieve the key I used to pack a channel?

Hopefully you have some old packages that used that key. They get downloaded somewhere when you click the pkg link, if you haven't removed them they might still be there. You can use that pkg to re-key the Roku to the old key.

edit: sorry if Eclipse does not work like this, I'm referring to the web utilities.

Yes, along the same lines as Squirreltown - if you packaged a second channel using the same key you can download your package for that to re-key from the "Manage my channels" link in the dev portal.

I must have pissed off many users of my IP Camera Viewer... for all channel updates I generated another key in Eclipse and only today I realized that with a new key you can't read the registry from prev. version, and to add a new camera takes a lot of typing with the Roku remote. 

At least in the latest version I submitted I implemented an "easy add" feature where they can use a browser to add the info... maybe they'll forgive my mistake 😉

I'll make sure to use the same key always from now on...

This is probably obvious, but note that if you've already published a version using a second key, then going back to the first key will cause another disruption for your users.  You should just stick with the last key you used.

FWIW, this is all explained in the Channel Packaging and Publishing doc, under Packaging Your Application.  The rekeying process is also explained there.

* Applications can share data via registry entries if and only if the applications are packaged with same key
* New versions of applications will have to re-link if they are packaged with a different key
* It is critical to save the password and keep track of the key that signed an application. If the password is lost, you will not be able to sign any new packages (including new versions) with the same key.

--Mark