Why is packagekit starting up throughout the day? There is no indication in the messages which component is sending the message to start packagekit, just a dbus message indicating that the service was started:
DISTRIB_RELEASE=12.04
DISTRIB_CODENAME=precise
DISTRIB_DESCRIPTION="Ubuntu 12.04.2 LTS"Syslog
AptDaemon.PackageKit: INFO: Initializing PackageKit compat layer
dbus[1207]: [system] Successfully activated service 'org.freedesktop.PackageKit'
AptDaemon.PackageKit: INFO: Initializing PackageKit transaction
AptDaemon.Worker: INFO: Simulating trans: /org/debian/apt/transaction/fbf7b3e9013a4a94a9bcf7a178f1d31e
AptDaemon.Worker: INFO: Processing transaction /org/debian/apt/transaction/fbf7b3e9013a4a94a9bcf7a178f1d31e1 Answer
That isn't PackageKit, but rather is a compatible API in aptdaemon such that things written with the PackageKit API to request installation of packages, and do so on Ubuntu, without having to support a different API.
If you look at /var/log/apt/history.log and find the correlating time for when this call happened, you should be able to see what the transaction was at least. If there is no correlating activity in there, it's likely something requesting a check for updates available to the system.
You could use the dbus-monitor tool in a terminal, filtering on the org.freedesktop.PackageKit service, to see what is making the call.
