After working with Time Capsule for several months, I've concluded that every Wi-Fi access point should have a built-in hard drive. One compact, passive cooled, AC-powered device not only houses an 802.11n access point with traditional capabilities, but it also has wireless bridge mode for one-click range expansion of an existing wireless network, easy administration from Windows and OS X, and 500 GB or 1 TB of internal storage published as a standard Windows and/or Mac shared volume. For individual users, Time Capsule can be used as a cable-free external hard drive. In commercial settings, all kinds of creative infrastructure options can be crafted by stringing Time Capsule and AirPort Extreme units together through your wired or wireless LAN.
In a business, branch office, point of sale, or SOHO setting, it is Time Capsule's combination of shared storage, network printing and extended WLAN that make the device a must-buy. I set up Time Capsule to extend a WLAN served by my existing AirPort Extreme (802.11n) base station. I plugged Time Capsule in and set it up with credentials for AirPort Extreme. When Time Capsule rebooted, the extended WLAN and internal storage were both on-line. I enjoy letting non-Apple-savvy visitors try to figure out what the white box with no cables (except for AC) is.
Time Capsule is not managed via HTTP, which turns out to be an advantage. I have never encountered a scenario that required me to use Ethernet to administer AirPort Extreme or Time Capsule; all administration, even of factory-reset devices, is wireless. Administrators are also automatically notified of firmware and AirPort Utility updates via Apple Software Update (OS X or Windows), and Time Capsule itself blinks its front panel LED when new firmware is available.
For wired use, Time Capsule has three gigabit Ethernet ports plus one port that links it to wired infrastructure or directly to a cable or DSL modem. Like AirPort Extreme, Time Capsule's DHCP server can operate in either NAT or bridge mode. In bridge mode, only the first static IP is exposed to the wireless network. My DSL has a five IP block, so I run AirPort Extreme in NAT mode with one of its static Internet IPs shared across clients. When Time Capsule is used to extend an existing network, the original base station distributes IP addresses and all traffic is passed to it, as you'd expect a bridge to do.
Time Capsule's storage model is simple, but adequate. The internal drive is published as a single, arbitrarily named volume spanning the entire physical drive. The volume can be mounted as a share by any SMB or AFP client. Each external USB drive is its own named volume. For backup, AirPort Utility has the handy facility of transferring the contents of Time Capsule's internal drive to an external USB drive. Time Capsule has no method for replication across units, but this can be accomplished with a trivial shell script.
As an alternative to default full-volume sharing, AirPort Utility lets you set up a user/password table that's used to grant users access to storage. When table authentication mode is used, each user listed in the table has exclusive access to a folder that bears their user name. Other users' folders are not only inaccessible, they're invisible. This makes administration in a group setting an interesting exercise. I prefer to use Time Capsule in its default mode, where a single password grants access to the entire volume, and guest (unauthenticated) users get read-only access. I drop all of the ISO images that I download from Microsoft and Apple developer programs, and images that I make of install CDs and DVDs, directly to Time Capsule, and I maintain fail-safe OS X built client and naked boot images there as well. I get this without having a server to manage.
Time Capsule is useful for a far broader range of usage scenarios than are obvious, more than I imagined from the specifications or the first weeks of using the product. The next time you buy an access point, save a few more pennies and spring for a Time Capsule.