On September 10, 2012, Google made it possible for mobile device users to edit Google documents from their mobile device - no PC needed.
On September 10, 2012, Google updated the iOS and Android versions of the Google Drive mobile app. iPhone and iPad users can now create and edit Google text documents in the app. Android users gained the ability to add and reply to comments. Users of both platforms can share documents with other people right from the mobile device.
Multi-user, real-time mobile editing
Google Drive's strength has always been collaborative online editing. These updates bring collaborative editing to your mobile devices. Yes, that's right: the Google Drive mobile apps give you multi-user, live, real-time text editing on your phone.
Create a document on your new iPhone. Share the document with a co-worker or client from your iPad. Edit the document on your Nexus 7, while they edit on their iPhone. No desktop or laptop needed: it doesn't get more "post-PC" than this. Mobile editing also works offline, although you have to turn a slider "on" to make a document available offline.
Figure Aunderline text on your mobile device. Numbered and bulleted lists work well, as do basic text alignment controls (left, right, centered or justified).
The design is clean and simple: black menus, gray controls, white background, and blue buttons. On iOS, the user can choose from ten fonts, ranging in size from 6 to 108 point. Mobile users can also change text and background colors, which helps draw attention to edits or items for discussion.
The number of words visible varies by device. The most text is visible on a desktop or laptop - which is not a surprise. Tablets are next. With Apple's Smart Cover, I find editing easiest with the iPad held horizontally - which decreases the number of lines one can see. Editing on the Nexus 7 is simplest held vertically (and by using the SwiftKey 3 keyboard). The Google Drive app on the iPhone 4S shows the least amount of text. I expect that Google will revise the app to take advantage of the additional screen space when the iPhone 5 is available.
Single-user, multi-device editing
A Google study in August 2012 found "sequential screening" to be common: people start a task on one device, and then complete the task on another. For many professionals, these screens include some combination of one or more work and/or home desktop, laptop, tablet, and smartphone. Google Drive enables "sequential screening" for writing tasks.
As a tech consultant, I frequently create a document on my Chromebox (desktop), and edit the document with my Chromebook (laptop) while seated in a client's office. At some point, I roam around the office to look at equipment. Editing on a laptop while standing is difficult; editing on a smartphone while standing is simple. And editing on a tablet while standing makes me feel like I'm on Star Trek.
(FWIW: I used Google Drive on all four of these devices to upload the above screenshots. I wrote and edited the post using all four devices, as well.)