A simple thing that every package management system should have
Here's something that I was reminded about recently, most directly due to doing some work on a Solaris machine (although the general issue has come up before).
Every single package management should provide a way to save the name and version information for all packages and patches (if you use them) that are installed on a system, and also a way of easily setting up another system with exactly that set of packages and patches. This should be done through straightforward command line tools; it should certainly not require installing or adopting a great big system management system, using a web frontend or management console, or whatever. Both of these tools should be installed by default.
Ideally these tools would produce and consume plain text in a straightforward format. If you insist on making your version of these tools use XML or some other private database format, you need to also provide tools that dump a readable form of this and report the differences between two package states.
(Sooner or later sysadmins are going to want both abilities.)
By the way, if your operating system or Linux distribution can't always recreate a given set of package versions for whatever reason, you cannot really aspire to being a 'production' or 'enterprise' ready operating system. One common reason is feeling that some updates are mandatory and so not giving people any option about those updates when they install new systems; another is removing old versions of packages or patches when newer versions are released.
(This means that I don't think that Fedora is production ready, since Fedora deletes the binary RPMs for obsoleted updates from mirrors. You can get around this by maintaining your own local Fedora mirror that never deletes anything. Note that I understand why Fedora does this, and being 'production ready' in this way is not part of Fedora's goals anyways. Red Hat Enterprise does keep all package versions around forever for exactly this reason.)