I don't know if Blizzard figured it would take a few weeks for someone to do it, but someone did and I was watching some of it last night. Player Alkaizer
managed to hit level 100 Paragon in Diablo III
making him one of the first if not the first to do so. He was streaming his play through Twitch.TV and you can watch his accomplishment
if you view the end of the Paragon 99 Barb video.
It was just crazy seeing him whirlwind and fight his way through all the enemies. He had helped with a friend who played when he wasn't and from what I can tell, they mostly played Act III. I even saw one enemy drop two legendary items, which is a real rarity.
I've screen capped his accomplishment as well as three chest tabs if you're curious as to what he's got. Congrats to Alkaizer for this achievement.