When i'm having to update a mac suite (10.5), as all clients are the same original image build and hardware type i sit at one, run software update locally on a client, select download packages only, copy them from the client (cant remember off top of my head where they get saved to) up onto the server and use ARD to push out the update packages as a remote install to the rest of the suite.
saves me logging into each machine and updates are still only downloaded the once, i keep them in a dated folder with the suite name for future reff also - not sure what would happen if an update was pushed out to a client and not required if it would force install it or not and cause a problem - but a bit of planning and checking and I've not had any problems doing this so far - not done this for a while though.
I kept the software update server pointing to an incorrect update source setting so the clients normally dont see any updates available to them and wont bug users with the 'update available for install' message on apps start up.
Just wish the Macs had a WSUS style arrangement, much better in my opinion.
Hope it helps