In some organizations, the IT administrators are somewhat paranoid. I have got a Windows 7 laptop with a non-editable screen saver timeout of 15 minutes. As I only use this laptop for the terminally-broken Outlook, it has the tendency to be locked-up all the time.
To avoid this syndrome, I tried to hack the registry. It worked until the next reboot, where the deployed policy broke my hack and returned the timeout to 15 minutes.
I then found out a nice solution in the form of caffeine. Put it in your auto-start folder and forget about the problem. And for the ones thinking I’m breaking the company policy, they are wrong. When I leave my place, I always lock my two screens manually. And yes, even to go to the printer. This is IMHO a much better way of ensuring the security of the servers and networks I can access from my machines than waiting 15 minutes until the screen saver starts.