This morning I waked up and I was thinking about the password on my phone. I've always found it annoying having to retype it every now and them, specially if I'm at a place like my home where no one else can grab it.
So I thought that the device should be smarter, and I think that currently it should be possible to bring a little intelligence to these "smartphones". When I'm at a place that I have to configured to be trusted, then once I unlock the phone it should remain unlocked as long as it remains there or I don't explicitly lock it.
One easy way to achieve this would be to enhance the wifi manager, whenever I connect to a protected wifi with a password one new option is available: "this is a trusted site", by checking it the phone (or any similar mobile device) will remain unlocked and it's also possible to specify if the unlock should last some minutes (5 or 10, like when you are doing something with 2 devices, leave one apart and when you pick it up again it's locked so you waste time unlocking it), one hour or remain unlocked as long as you're connected.
That simple change could help lots of times, if we can use the devices at home without the need to retype the password (or whatever lock mechanism you've chosen), then we would be slightly happier and we could use slightly harder passwords for the moments when we're out of home.
Additional refinements could defined as an option to specify a coverage zone: instead of home, you're at work in your office, so you want the device to remain unlocked while you're there, but if you move out of the office then it should go back to the normal behavior.
I think that many people might not be using currently any password just to avoid the hassle of having to unlock his device every now and then, but if a system like the proposed in this post would be available then I would bet that they would be much happier to know that they have a secure device when they're walking down the streets while keeping the simplicity of an always available device at home without the need to retype the password at every moment.