I must admit, I have an irrational fear of firmware updates.

The Time Capsule and AirPort Base Station (802.11n) Firmware 7.3.2 update requires that you already have AirPort Utility 5.3.2 installed (versions for Leopard, Tiger and Windows are available).

What does it do? Well, let's see what Apple has to say...
The Time Capsule, AirPort Extreme and AirPort Express Base Station with 802.11n* Firmware 7.3.2 updates include bug fixes.
Hmm...bug fixes. That should take care of anyone who found the write ups on the other updates too exhaustive but it doesn't ease my fears.