Yesterday, somebody asked me on IRC if there was a list of projects using PackageKit. I said no. I’m now adding a section on the website with just this content.
So, please send an email to me or the mailing list if your project is using PackageKit BY DEFAULT. This doesn’t mean “can be installed on”, but means “is usable when freshly installed”. I think it makes sense to add projects like nautilus that hook into the session interface too.