Screensavers are an interesting case. We have a good idea of whether most hardware is "doing something" or not, based on whether it's generating traffic or an application has it open. This is less true of screens - the resource making use of the display is the user, and it's entirely possible for the user to be reading or watching something onscreen without us getting any feedback from them. It's common to see people noticing that their screensaver is activating and hitting the mouse or keyboard to stop it. What's the correct solution?
One solution is to have the user increase the screensaver timeout. This is a poor solution - it's one of those "Think about what you're going to be doing with the computer before starting to do it" ideas that I dislike a lot. Computers are there to serve the user, not the other way around. The other downside to this is that the timeout will be left at a large number and monitors will be turned on for significantly longer than necessary.
Another is to pay attention to what the user's doing. If they keep hitting the keyboard just as the screensaver's activating, it's because they want a larger timeout. It's not difficult to give them that. I spent a while today playing with various complex implementations, but I finally came down to a simple one:
- If the user generates activity while the screen is blanking or immediately afterwards, bump the timeout by 10 minutes. Perform a further increase each time they do this.
- If the screen is successfully blanked and the user doesn't immediately unblank it, reset the timeout to the original value
To test this out, I've actually gone to the extent of setting my default screensaver timeout to a minute. We'll see whether it gets irritating. I suspect that there's some more fine tuning to do, and I may want some kind of decay function rather than immediately pushing the timeout back to the original value.
Next job is to think about whether there's any reason to not just enter DPMS straight away if the user's selected a blank screen...
 I'm thinking along the lines of IRC conversations or logfiles rather than films - media players should be talking to the screensaver already