One of the announced features of iCloud is the ability to keep all your files from Apple's Pages, Numbers, and Keynote apps up to date. The update to those apps that bring this support is now available.
I am particularly excited about using Numbers with iCloud. I use Numbers on my iPad to record my students' grades, but sometimes I forget to bring my iPad to class. It never fails that those are the days that a student notices that I made a mistake and needs a grade changed. Before iCloud, I would make a note in my notes app and make the change later. Now, I'll just open the spreadsheet with Numbers on my iPhone, make the change, and it will be reflected on the spreadsheet on my iPad. Win.