When I start a new KDE session just after a boot sequence on Fedora, Packagekit saturates my DSL network bandwidth (~ 230 ko) during several minutes due to the ratio : data size to download versus the available bandwidth.
This behaviour, like desktop indexing, prevent to use its computer in a comfortable way in the first 10 minutes, which is painful when you need to something quickly, like browsing a web service requiring a reactive data transfer.
PackageKit must have an option to limit and delay the downloading for those who do not have a fast connection.
We moved the upstream bugtracker to GitHub a long time ago. If this issue still affects you please re-create the issue here: https://github.com/hughsie/PackageKit/issues
Sorry for the impersonal message, and fingers crossed your issue no longer happens. Thanks.