While I don't have a use for this, I do like the idea of purposeful modes in computing. Obviously there is a lot you can do with shortcuts and preferences, but its nice to have a limited to base to start with.

I think this is even more important with a mobile platform since for one, battery and processing power is at a premium, and two anything with notifications could take you out of your desired "mode" if you don't wrangle them properly.

Something I've always wanted in a smartphone is to be able to boot into a "camera only" mode. There have been many times where all I need my phone for is as a camera, and I don't want it wasting resources/battery doing anything else. If this mode were light enough, it could boot up in the same amount of time as a normal digital camera, allowing your the phone to be truly off while you're not taking pictures. I do often take a digital camera with me, but sometimes I don't want the bulk or maybe I didn't initially plan to take a lot of pictures.