I've done some ethnographic research of mobile web-browsing and the key thing that I have found is that mobile browsing tends to be around quick checking (of a fact, like train or movie times) and laptop and tablet browsing tends to be mode around reading longer content, such as news or magazine articles. Mobile is more reactionary and users tend to spend less time reading and more time skimming.
Now, some BIG caveats to what I have observed: mobile browsers are getting better all the time, with the latest innovation being a "reader" mode that strips away the style sheets and nav and allows the user to focus on just the content (this is coming in iOS 5) – this mode really supports reading activity and I think will lead to more prolonged web content consumption on the mobile device. Additionally, the research I have done was over a year ago and in the mobile space habits are changing rapidly, as new innovations and technology enter the market (a good example being high-end display screens that render text much easier on the eyes).