TL;DR -- Admin > View (+create new) > Filters (+new) > "include only" + "traffic to the hostname" + "that contain" + 'subdomain.host.com'
In order to track multiple subdomains with Google's new Universal Analytics, you can include the same tracking code (the "isogram" version) on any page with no special configuration. But in order to report on it properly, you have to filter it using Views; otherwise the default is to show all website(s) data in one report.
The key seems to be that the View Filter must contain (or possibly start with) the subdomain, rather than equals exactly.
(props to source for pointing it out, just not as succinctly)