The Google Chrome webbrowser has always had automatic updates, and Firefox is heading that way in 2012. Now Microsoft is to join the party and where users have Automatic Updates enabled on a Windows machine they can expect an update to the latest web browser available for their operating system.
The problem with Automatic Updates from any application is that they are invariably unaware of any billing implications. This means that many road warriors have Automatic Updates turned off, to avoid using up precious mobile broadband allowance when travelling. The biggest danger will occur when roaming outside the EU, where just 1 MB of data can end up costing several pounds.
Australia and Brazil are slated to be the first countries to receive these updates in 2012, so any adverse impact should be detected first in those countries. The most likely problems will be for people who have automatic updates enabled to ensure the Operating System is patched, and after upgrading their find some web pages don't work, or due to the large number of DLL's involved in an Internet Explorer update, they may find other applications crash more often (e.g. applications using MSHTML.DLL).
All those reading this who act as family IT support, with Christmas coming up, it may be worth checking what is running on various machines and pre-emptively updating them while visiting over the Christmas break, particularly as you can then explain the various changes to their web browser. Even if you have installed an alternative browser on their computer, it is worth checking what will happen when Internet Explorer is not the default browser and the update is pushed at them.