Internet tablets used to have a "secret" mode, called "softpoweroff", which would lock screen and keys, stop all wireless services, put the processor into power saving mode (except if stuff like a music player is running) and blank the screen.

It was relatively easy to remap the powerkey to invoke softpoweroff, if you knew how to use an editor and how to use the search function of this forum (my tablet invokes softpoweroff on a long press on the power button). However, Nokia "chose" to b0rk up softpoweroff on ITOS2008, so now you have to install Powerlaunch and learn a complete and arcane programming language to get back functionality that was there before.