Wii System Menu 4.2 was released yesterday.
Summary of changes (non homebrew-wise):
Wii Shop Channel has had an update that stops any Wii's not updated to System Menu 4.2 from accessing it.
and
"This update provides behind-the-scenes fixes that will not affect features but will improve the overall system performance. "

Summary of changes (homebrew-wise)
Bannerbomb doesn't work so use Smash Stack or Indiana Pwns as a workaround (Bannerbomb will get an update soon)

Updated boot2 to boot2v4 which BootMii uses, use Hackmii installer v0.5 (re)install

Homebrew channel v1.04 and less is deleted, v1.05 isn't deleted when updated. Use Hackmii installer v0.5 to (re)install or update to v1.05 if you already installed HBC.

Most of the IOSs used by cIOS can't be used so basically don't pirate.

DVDx is deleted so use Hackmii v0.5


In general updating isn't recommended at all due to reports of Wii's getting bricked (even if you haven't installed homebrew on your Wii)

I'll wait until I'll need to go on the shop (which will be soon because I'll be buying Rumble and getting a free NES game as a refund) before I start messing with any updates. As it's less than two days old, I'll just wait for the homebrew community to have well-working updates and installers before bothering with a half-working HBC and a possibly bricked Wii.

Never used Bannerbomb, just used Twlight hack, TWLIGHT HACK FOREVA

For those of you who haven't updated yet, don't bother yet (even if you don't have HC). It seems the update is bricking normal Wii's that haven't been modded or had the HC installed.

It didn't brick my Wii, still working fine. Unless...

Little anecdote here, this reminds me of the PlayStation Home's 3.0 update. It recently launched and there was a notable YouTube video I saw that showed the update crash some poor sap's 'net router, the PS3, the guy's wireless network in its entireity (creating a strange on and off loop of reconnection and disconnection) and eventually caused the dude's PS3 to burst into mild flame.