I'd like to write a plugin that can handle URLs to .deb packages that will download the .deb to a temporary location and then open the .deb with Application Manager (after a warning if the .deb comes from a non-repository location).

Also, the same plugin should be able to handle text/data that just describes a package name and downloads and installs it from the repository using the Application Manager (what's the best way to "encode" information like this and have it detected by mbarcode as a package name?).

Someone could then provide a web interface to generate such QR codes and publish them on the application web pages (maybe we can even get these "app codes" integrated into maemo.org/downloads).

This is a well-known technique for installing apps in the Android world, and I think it would be a nice way of quickly "discovering" apps on Maemo, too.