What are the biggest configuration management challenges?
Summary: today I had an operations managmenet guy ask me what the biggest challenges of configuration management are. I gave my usual 'it depends' qualifier, but soon focused on client health management and management points.
I was right - it does depend. On a small or medium scale, management points will be simple (there will be just one per site, and they'll be on the site server). And on a small scale either client health management doesn't matter or you go and look at the client to see what state it's in. But on larger scales those issues can become tricky.
I would like to edit my answer: configuration management is also a 'many moving parts' problem. Operations management has the benefit of usually being done for datacenter servers that are non-mobile, generally at the end of fast links, require limited services (what I call 'eventing'), and are almost always 'up'. They're also expensive, so the scale is smaller. Configuration management doesn't generally have those advantages. So configuration management has to be done with a lot of distributed servers, often in complicated environments, and they have to provide more services (numerous variations on inventory collection, discovery, software installatin, patch scanning and installation, status messaging, state messaging, software metering, remoting, etc.).
Any system with lots of moving parts is going to be challenging. Planning, deployment, monitoring, reporting, troubleshooting, administration, testing, and usage are all that much more complicated.
So the biggest configuration management challenge is the 'many moving parts' problem.
p.s. The other challenge I would add to my original answer is that configuration management is its interest to a wider audience. Operations management is interesting to server owners, service managers, security, and administrators - generally technically people. Configuration management, with its large desktop component, is also interesting to anyone involved in desktops, including general management, asset managers, and end-users. So there is also the 'many interested parties' problem - how do we explain all our challenges to such a wide variety of interested parties?