Since people are increasingly using their mobile devices as personal computers, using email, storing corporate and confidential data, the security of these information became a high priority requirement.
However, there is a trade-off between security and usability. It is very easy to protect the (touch) screen to prevent the system to do some undesirable action. But adding a security layer to this mechanism (to avoid curious ppl) sometimes is not a good experience for the user.
I think the Maemo could give to the user the flexibility to choose the way of how to lock or unlock his device. Currently he can use a registered 'pin' number, but for many people, make a gesture on the screen would be faster, easier to decorate and more friendly.
Note: lock screen != lock device
lock screen -> to prevent undesirable actions (touches) on the screen.
lock device -> to prevent malicious or curious people to access the device data.
Discussion thread: http://talk.maemo.org/showthread.php?p=354985