The udpate includes:
USB keyboard support in Mii Channel.
Enhanced parental controls.
Dramatically increased SD transfer speeds
New IOS50 and IOS254.
System Menu now runs on IOS50.
IOS254 was added to remove "PatchMii Core".
Patched to resist
Twilight Hack 0.1beta1.
The SD transfer speed is apparently a significant speed boost. A 360 block Wiiware game can be transfered in 30 seconds as opposed to 15 minutes previously. I'm not sure if this is true, but i shall see when I'm playing World Tour tonight if it significantly speeds up DLC stuff.