Airport Time Capsule considered harmful
The premise of the Apple ecosystem is "It just works." It is a world of hardware and software in which you pay a premium for not having to worry about fiddling with configurations and command-line options and incompatibility.
The Airport Time Capsule is a wireless router that also contains a hard drive for backups and media sharing. Bizarrely, though, the hard drive it contains is not accessible to OS X's Drive Utility program, so a run-of-the-mill filesystem error can cause the disk to be inaccessible. It's the antithesis of "It Just Works." It's "It Just Will Not Work."
Don't buy an Airport Time Capsule.