This one is the real interesting, one how can subscribe to enhanced presence. See also Subscriptions in UCMA part 3: Presence
The sample code here shows how to subscribe to one user. Actually this is a batch subscribe and is easy extensible for multiple users.
This one is much more complex then subscribing to presence using PIDF. The real thing here is enhanced presence. You can subscribe to multiple categories.
more see the new Unified Communications Development weblog.