This morning when I turned on my Wii U it started updating. The update, according to Nintendo, offers "further improvements to overall system stability and other minor adjustments." There have been rumors that Nintendo is working on improving the Wii U's wretchedly slow menu load time, but this update doesn't appear to do that. Some people are optimistically claiming load times are faster now, but one reddit user who apparently likes to time things says that his load times are generally unchanged, and that's my less methodical opinion as well.
There are surprisingly varied reports on how long this update takes. In my case I'd say it took perhaps 10 minutes to download and 15 to install, but others are claiming updates taking anywhere from 10 minutes to an hour.
Hopefully this will lessen issues with the Wii U freezing, although that's a problem I had at first that just seemed to go away on its own.