Does Power Nap work for multiple users?
Power Nap will receive user level data for any users that are logged in. If you have fast user switching enabled and both accounts are logged in when the Mac goes to sleep, both should get updates.

If there is a bug, it could be reported, but in the light testing I've done, everything seems to work well for users that have logged in.

If the user is not logged in, updates currently do not occur (OS X v10.8.2).