It's unclear if that local space is shared with others that might be logging in after you though.
Really cool concept overall, but there's a good amount of uncertainty in there. There's a handful of gramatical errors too, so maybe they aren't really ready to launch?
Why wouldn't it be like unix where each user has their stuff in their home directory. OSX already has this concept with user switching. This just allows you to login as multiple users on an OSX machine at the same time.
Edit - looks like there is persistent on-VM storage, from the homepage: "In additional to local hard drive space..."