Daring Fireball highlights a new support document from Apple addressing the issue of "unsupported third-party digital media players" syncing with iTunes. The brief document warns users that Apple does not test its software with such devices and thus their ability to sync with iTunes may be broken by future software updates.
Apple is aware that some third-parties claim that their digital media players are able to sync with Apple software. However, Apple does not provide support for, or test for compatibility with, non-Apple digital media players and, because software changes over time, newer versions of Apple's iTunes software may no longer provide syncing functionality with non-Apple digital media players.
The new Palm Pre has received a significant amount of attention for its ability to sync with iTunes despite the lack of support from Apple. The Pre has been discovered to accomplish this feat by emulating an iPod by transmitting Apple-specific vendor and product IDs to iTunes.