The current iPhone OS SDK contains no official API support for USB syncing apps, but that hasn’t stopped persistent developers from getting around the issue by dropping their files into the iPhone’s DCIM folder and using private APIs to allow desktop apps to access your iPhone’s contents.
It was a hack, and developers knew Apple wouldn’t tolerate it forever, which makes it no surprise that several developers (including the makers of the popular e-reading app, Stanza, are now reporting that Apple is asking them to remove USB syncing capabilities from their apps.
This is a temporary inconvenience, but not really a bad thing. The beta SDK for iPhone OS 3.2 has official APIs for accessing an on-device shared storage folder, which will allows an iPhone to be mounted as a readable and writable disk when plugged into a computer through USB.
End result? Official, less buggy USB app syncing support come the end of March. Just don’t upgrade any apps that currently use the DCIM method of USB syncing until iPhone OS 3.2 hits iTunes.