Even though the 10.5.2 update has fixed many problems, one of the functions that was announced with Leopard but is still not available is using an external disc connected to Airport Extreme N devices, for backups etc.
This functionality was still available in the 10.5 betas, but has been pulled out in the released version. In fact, it appears that the backups can become corrupt, without informing the user about it.
We can only hope now that a firmware update for the device will fix this important and practical functionality, especially for laptops. This might happen at the end of the month when Time Capsule is released, which is actually nothing more than an Airport base station with integrated HDD.
[translation by xavier]