The port itself is durable provided you do not jam in items that don't belong there. Besides having an iPhone 4, iPod Touch, I have many iPods including one from 2003 with Dock connector that still sees heavy use. The port on that works flawlessly for all cables I have, including a new Universal dock. To this day since 2003, I have yet to have a Dock port break on a device.
Just be sure to avoid having coins, or other items in your pocket that could possibly find themselves wedged in that port, or other places. Besides possibly scratching the phone, the port could potentially get damaged.