A post on the Diablo III Forums (and
this follow up post) outline an exploit to make Wizards invulnerable in Blizzard's action/RPG sequel. The first post originally outlined how to perform the exploit, but that was later edited out of the post, and while there are a bunch of posts suggesting this is not true, there are at least as many saying it is, as well as a video of someone showing the it in action. The latest posts in the thread include arguments over whether or not this has now been addressed by a hotfix.
Update: The now-closed thread includes this post from Blizzard: "Thanks for your reports guys! We'll get this addressed."