Description of problem: yum-updatesd is not installed when an update from fc5 to fc6 is done. Furthermore puplet is not started by default when logging in to GNOME or KDE. How reproducible: I observed this on two systems which were updated accordingly.
I can confirm the first part of this at least. I upgraded a server from FC5 to FC6 and noticed that no nightly updates were happening. I checked and /etc/init.d/yum wasn't present. After installing the yum-updatesd rpm I get an entry back in /etc/init.d and my nightly updates are working again. I suppose it's too late to do anything about this now, but users should at least be made aware that they might not be getting their updates.
New features are generally not installed on an upgrade. And unfortunately, requiring it would end up meaning breaking people who don't want it installed (for various reasons)