There are currently two major issues Blizzard has announced.
The first is a series of display problems, which Blizzard recommends you do the standard deleting of the WTF, Cache, and Interface folders. Before you do that be aware that removing the folders will delete all your add-ons and add-on preferences. In my experience, you're better off deleting the Cache folder and then updating all your add-ons, or just disabling add-ons which are out of date.
More detailed instructions for Windows and MacOS X can be found in Syndri's post on the official forums.
The other issue that items which are tradable under the BoP rules are not able to be socketed. This appears to not be affecting everyone, however there is a work around in the following steps: