Not only does the IPv6 module take around 250k of memory, it has also been reported that disabling the feature notoriously speeds up network access for programs that erroneously try to query servers with this newer version. Incidentally, Firefox is listed among the affected applications. So until the widespread adoption of IPv6, one may benefit by disabling the module.
Since Arch's official kernel26 package version 126.96.36.199-1, IPv6 is no longer compiled directly into the kernel, but as a module entitled ipv6. Many users don't require the features, and may benefit from added performance (many programs will query IPv6 addresses first, unaware that you don't have an IPv6 connection) and more free memory (250k, that's a mighty big module) if removed.
Method 1: Disable until needed
The ipv6 module is normally loaded at boot. There are many programs which will also load the ipv6 module after the system has booted if they detect that it is available. In fact, these programs load net-pf-10, which is an alias to ipv6. You may wish to stop all such activity. Adding the following line to Template:Filename will disable the automatic loading of ipv6, but will still allow you to load it manually if needed.
# disable autoload of ipv6 alias net-pf-10 off
Method 2: Disable entirely
An alternative method is to disable the module completely by adding the following to Template:Filename:
options ipv6 disable=1
Disable IPv6 during pre-init process
ipv6 - kernel.org Documentation