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page 3 of the Ars article
One of the benefits of iWork on the Mac is that content from one app can be easily included in documents for the others. For instance, you could include a chart based on data from a Numbers spreadsheet in a Keynote presentation. When that data is updated in the spreadsheet, the chart can be automatically updated in Keynote. If documents were sequestered away from each other on the iPad, you wouldn't be able to do this. Furthermore, how would you get your iWork files onto the iPad for editing, and how would you get files created on the iPad back to your Mac?

Thankfully, Apple has addressed this in the iPad-only iPhone OS 3.2. The documentation for the SDK indicates that it uses a "shared folder" that any iPad application can read and write. This shared folder will also mount as a disk whenever an iPad is plugged in to a Mac or PC, allowing easy file transfer.

This shared folder solves the problem of transferring files, and allowing one app to read data from other app's files. Nonetheless, Apple could take this capability and extend it further. Apple could leverage iDisk to keep this shared folder in sync between a Mac and an iPad over-the-air, instead of relying solely on a wired, USB connection.