I'll tell you this from a user perspective (But also one that has worked in IT). Screensavers and application time outs SUCK. They are a major annoyance and impede on productivity, and serve little to no purpose. While I'm sitting at my PC I don't want crap constantly timing out on me, there is zero use to that from a security stand point. The proper thing to do is to ensure that users lock their PC when they step away.
Instead of forcing time outs on people, ensure that when they step away, they lock their PC. When an app times out, or screensaver comes on, users just shake the mouse or log back in. So for about 1 second or maybe 1 minute the app will be locked, otherwise it will be unlocked. That 1 minute of the app being locked is not going to mean much.
If someone happens to come in the building and puts a gun to my head to login to something, it does not matter if it locks or not, chances are I'll just comply and log in to it anyway.
For a while they were forcing a screensaver GPO on us so I wrote a program that toggles the scroll lock key and gave it to everyone. If that had not worked we would have come up with a hardware solution such as a spinning mirror to put under the mouse. In a way the hardware solution is probably better as it does not involve potentially breaching any kind of rules about unauthorized software. Thankfully our manager pushed IT to ensure they remove the GPO from our PCs. Though we still have to fight with lot of apps that time out, which is just as bad, if worse, than screensavers. I'd say a good percentage of my job is spent reviving apps that have timed out. These time outs serve no purpose from a security standpoint and are simply an annoyance.
Sounds great, although how do we ensure users lock their PC's when they step away?
If only there was some mechanism where we could lock it after a certain time in case they forget to lock it when they walk away.....