Google has added the capability to both create and edit spreadsheets to its Google Drive apps, so you can now calculate and tally up whatever you like in a spreadsheet while out on the go. Users could previously browse shared spreadsheets on the app, but the latest update, for version 1.2.0, brings full spreadsheet editing capability in for all users.
The update also adds a new screen to view recent Drive uploads, and you can also now upload to Google Drive directly from a mobile device. Just use the "Open in..." feature in whatever app your document is currently sitting in, and Google Drive should appear as an option. Open it up there, and the doc will automatically be uploaded to Google's cloud service.
Pretty snazzy. Of course, Google Drive remains a free service (at least to start) and the app is still a free download.