Mac users of OSX should click on the Apple menu and select SOFTWARE UPDATE. Your system will automatically connect to Apple's update site and download and install the files necessary to update your system.
This update is for users of OSX.3 only.
I think it's better to download the combo installer and burn it - then you can get back to a full-load quicker, if you have to do a reinstall, than reloading 10.3 and waiting to download the updater again (especially if you have a sucky download speed). Every time I do an updater download I end up passing it on to several people who DO have slow connections.
Anyways, I'll wait on an updater for 2-3 weeks and see how many howls it elicits as 'test subjects' start using it immediately (there are several sites that post new-OS bug finds).