The big problem is that iTunes does this poorly, with lots of bugs in its implementations. Worst of all, you cannot directly access files from iTunes to edit those documents in-place. Think about it: You offload a text document to your iPad, make some in-place edits, and want to continue updating that document on your Mac until you next hit the road.
Enter Ecamm. The company, well known for its Mac and iPhone utilities, has released the first version of its PadSync tool. PadSync, which retails for $9.95, offers direct access to your iPad Documents folders from a desktop Mac application. As the gallery here shows, your shared files are accessible on an app-by-app basis. Double-click on a Word file, and you can open it in Microsoft Word, edit it, and save it back.
Updates on the Mac instantly sync back to the iPad -- with one exception. Ecamm is still working on subfolder support, such as the Inbox that's created by the 3.2-and-later document sharing classes. Beyond that, PadSync offers all the instant synchronization you could wish for. Oh, and don't forget my favorite feature: since files are mirrored as well as synced on the Mac, you can access those files and queue up new ones even when the iPad is not connected to the Mac.
PadSync offers a 7 day free demo, so you can test out the app before purchase.