InformationWeek has a nice way (from Google) to describe mobile usage:
Google breaks down mobile users into three behavior groups:
A. “Repetitive now”
B. “Bored now”
C. “Urgent now”
The “bored now” are users who have time on their hands. People on trains or waiting in airports or sitting in cafes. Mobile users in this behavior group look a lot more like casual Web surfers, but mobile phones don’t offer the robust user input of a desktop, so the applications have to be tailored.
The “urgent now” is a request to find something specific fast, like the location of a bakery or directions to the airport. Since a lot of these questions are location-aware, Google tries to build location into the mobile versions of these queries.