I think you wouldn't be pleased if some unimportant call or, what is much worse, SPAM SMS message wakes you up. Solution would be to switch silent profile when you sleep. You can do it by hand ever day, but why not to automate it? You can use silencer, but it has very simple logic, which silences phone when it is late, but not when you sleep. What about something more intelligent? This is second article about ET-Prolog. First article was not rated high, i suspect because nobody understood how to work with it. So here is a practical example. You would need ET-Prolog to run programs, described here. New version of ET-Prolog already includes code, described here.

Simple silencer approach

Ensure, that your et-prolog/init.pl contains It is general initialization needed for most cases. Add following code to et-prolog/init.pl: It says, that we need new temporal term called "time to sleep" which becomes true at 23:00 and becomes false at 10:00. When it changes value et-prolog/simple_silent_sleep.pl should be executed. Save init.pl and start editing et-prolog/simple_silent_sleep.pl This means: if it is time to sleep now, but was not a moment ago or it is time to sleep and we don't know what was a moment ago, switch to silent profile. if it is not time to sleep now, but was a moment ago or it is not time to sleep and we don't know what was a moment ago, switch to general profile.
That's all. It took only 15 lines of code.

Making things complicated

I don't always go to bed at 23:00 and stand up at 10. But I usually set alarm, when I get up early and I switch light when I go to bed. So I want my phone switch to general profile when alarm rings, or at 10:00 if I haven't set an alarm. And I want it to go to silent mode not at 23:00 but after 23:00 when it becomes dark (remember, that we have ambient light sensor). This program would be much more complicated, about two screens of code, but still much less than it would take on usual programming language.
Ensure, that your et-prolog/init.pl contains Add following code to et-prolog/init.pl: Here we define several temporal terms and set up actions, that should be taken when these terms change value or are equal/less than specific value. We also register DBus listener which is needed for catching alarms. Let's start with helper scripts.

Catchng alarm

et-prolog/notification_eval.pl should contain If the first argument of received event is 'notify-clock-alarm', change 'alarm ringing' value to true and then to false. Alarm ringing would be true only during one epoch. This is how events are modeled in ET-Prolog.

Waiting for dark

et-prolog/wait_for_dark.pl should contain You have already seen similar code in simple example. If 'wait for dark' has changed from false to true then start polling light sensor once a minute and call et-prolog/silent_sleep.pl if it is less, than 50. Additional guard with empty script name is needed because ET-Prolog may forget temporal terms values if there are no scripts interested in them.
If 'wait for dark' has changed from true to false, then we don't need to watch for light sensor.

Switching profiles

et-prolog/sleep_profile.pl should contain The same scheme. If user sleeps now but didn't sleep before, switch to silent profile. And switch to general profile when user stops sleeping. Notice, that if user changes profile manually when phone thinks, that he is sleeping, profile would remain general. So you can make phone understand, that this night it should wake you up.

Main logic

et-prolog/silent_sleep.pl should contain Alarm means, that user is not sleeping. addHint('wait for dark',false) was added in a case if alarm rang when ET-Prolog was only waiting untill it becomes dark. If we won't do it, light sensor would still be polled and it would drain your battery. If one of these terms has other value this subgoal would not succeed and ET-Prolog would process next alternative. When program starts there is no information about previous epochs, so always(...) would succeed. That's why we ensure, that we have epoch older than 300 seconds. We just add hints. If it would lead to temporal term values changes, than guards would work and needed scripts would be run automatically. We have 'slept' term which is true, when user has already slept at this day, so we should not expect him to sleep again even if it is still early morning. Following true is just to make this goal succeed if we don't need to perform any actions.

Future improvements

When I go to bed it is usually silent around. So phone could use it microphone to check, that I'm sleeping. But I didn't have time to implement ambient noise level term in ET-Prolog.
It is not pleasant to find out, that phone has discharged at night and you don't have a time to charge it. If phone's battery is low and I went to bed I can ask me to charge it, before i fall asleep.
If there was answering machine application for n900 it would be possible to warn caller that user is sleeping, give him a time to decline call and if he didn't threat call as urgent and ring.