And in a nutshell:
This update does the following:
Make the Menus look cooler
Make the Menus load a bit faster
Mess up OpenWii (So don't update if you have OpenWii)
Stop you from using config discs (for the most part)
Wiikey, CycloWiz, Wiinja v2 & Deluxe are Unaffected
AR and Freeloader don't work
There are two updates for Version 3.0U - The first gives you the digital clock, and the disc channel icon, and changes the layout of the shop channel. The Second update changes the weather channel to show the forcast from the wii menu.
What do you base your suggestion that the 3.0 update messes up Wii's with OpenWii on? The one single post that was made on this forum by a guy who has failed to post any more info since? I'm very interested in this since I have a Wii with OpenWii myself, but we shouldn't spread rumors based on a single post by some dude until we have more evidence.
By the way I've read a post on the OpenWii board where some guy said his OpenWii runs fine after installing the new update.
I double dare you to upgrade. Prove the other guy wrong and become a legend.
What's the point? I can live without the new clock and "faster" channel loading times. Unless there is a game I want to play that requires me to update I dont see any reason to jump the gun on this one. However I would like to know if it definitely bricks the OpenWii or not.
My proof:
http://gbatemp.net/?act=ST&f=101&t=57174
QUOTE
  Wii 3.0 Update
Nintendo Getting Modchip Serious
user posted image
Wii Update 3.0 marks the most significant system change since the Wii's launch. It also shows that Nintendo are getting modchip conscious as there is now a new warning screen when updating that says having "an unauthorised technical modification" may brick your system.
Early reports show that the latest update does not brick systems with modchips, however some setup discs like the Wiikey setup disc have been rendered inoperable (however you can still use it by booting GCos first then loading the wiikey disc through that). This shows that Nintendo have indeed changed something under the hood, so modchip users should be wary of updating just yet.
Apart from modchip scares the update most noticeably sped up changing between channels and added in a digital clock. The Wii Shop channel has been redesigned and there are numerous other changes to Wii channel's and the message board. There is also speculation that the Wii's fan remains active when the console is switched off if Wiiconnect24 is enabled; to stop the Wii from heating up.
 (Changelog)
CODE
Channels:
-Digital Clock added to the Wii Menu right under the channel bar
-Forecast Channel now displays the current condition (cloudy, raining, etc.) directly in the Wii Menu in the Forecast Channel box
-News Channel can now show 2 scrolling headlines at a time in the Wii Menu, 3 when you click on the button
-Message Board now has the “Today’s Accomplishments” message as a white message which allows it to stand out from other messages
-Address Book entries can now be shifted around using A+B but only to empty spaces. Not too convenient.
-Calendar in Message Board no longer shows “Today’s Accomplishment” only days as having messages
-Scrolling messages in the Message Board now uses a different sound
Wii Shop Channel Overhauled (Visual aesthetic is the same, changes made to organization and browsing methods mostly)
-New Welcome screen detailing 4 Recommended Titles and the points they cost (gone is the title screen bar that had linkable games). The title bar can be clicked on to bring up a list of 20 recommended games.
-Titles You’ve Downloaded was moved to the main shop menu
-New ways to browse
-Popular Titles (2 pages of 10 and includes launch games so not only based on recent info)
-Newest Additions remains the same
-Search for a title which can use partial names
-Search by Category
-System shows the different systems and how many titles have been released under each
-Publisher showing different publishers and amount of titles released
-Genre (different genres listed and amount of titles under each)