I thought I might add a different perspective to the discussion: Education.
I'm new to the corporate world as I have been in public education for nearly 12 years prior to last month (as a DBA). The school district I left was one of the premier districts in the nation for technology use and many districts around the nation looked to us for advice. We used a standard image for all of our computers for many reasons with centralized management:
1. Sheer volume. We had 33,000+ desktop PCs and more than 5,000 laptops. Add to that 6,000+ administrative staff plus nearly 54,000 students...
2. Just plain dumb users. Even the younger generation of teachers coming to our district found it a challenge to turn it on much less be productive.
3. Students. I can say most were very respectful of the equipment and services we provided. There were some, though, that had malicious intent when they logged into the computer. One student in particular, managed to do enough damage that the campus had to have all of the computers re-imaged as well as restoring the servers to a backup point nearly eight weeks prior.
4. With the number of PCs provided continually increasing, a standard image allowed us to provide that to the hardware vendor so all new machines were simply "plug and play."
In my environment now, with only 270 employees, I think a less managed environment could be justified but some things, such as patch and security maintenance, still need to fall on the IT department. It is our job to make sure that the user experience is 100% every time they sit down at their computers.