Is there a way to power down an AirPort Time Capsule gracefully?
According to Apple (from the Time Capsule manual)
Using Your AirPort Time Capsule Safely
- The only way to shut off power completely to your AirPort Time Capsule is to disconnect it from the power source.
If you want to go above and beyond, you can be sure that all users all logged off, and not performing a backup through the Airport Utility, but this is not necessary...
For my AirPort Extreme, I use Airport Utility to restart the Airport, watch for the lights on the front, at the lights off phase I pull the plug, just slightly more graceful.