Shroud of the Avatar is using Unity--and, as I said earlier, they are going to he "one giant world" route with seamless phasing/servers (Like WoW recently did.)...So in essence everyone plays on the same shard, but they are phased in as it becomes less crowded or based on a set of parameters guessing their need (Like shop owners are always phased in for everyone when in the town with their shop).
It's a pretty ambitious MMO system, that, as far as I know, only Blizzard has been able to do. If they can do it with unity, it will be a pretty epic proving of it's ability to make not just an MMO but a massive online infrastructure.