Why is it aufs instead of unionfs? Not that I have a preference for either but I am curious :)
Docker isn't tied to aufs, if unionfs or any other union file system comes along and is better, we are more then happy to switch to it.
I'm using unionfs and while I'm not taxing it very much I haven't seen any issues so far. I'd love to know what to look out for. Is it easy to setup aufs?