Today a call went out for botnets to join, and yes - computers that have been hijacked. That doesn't prevent the owner from using the machine, though.
Most of this has been with a voluntary botnet. The volunteers download the software, configure it to take instructions from the hive and rock and roll!
-t
If they're volunteering that's fine. The hijacking thing is a real problem, it doesn't matter if they can still use the machine. Kind of like in Dark Night.