Leave it to Microsoft to release an SP1 when I'm on a business trip and unable to connect to my server for a couple of days. :(
In any event, if you missed the news, Office 2003 and OneNote SP1 is available at office online. Use the link to check for updates on the Help menu in any Office product.
Is it worth downloading it now? I think so. Outlook probably has the most fixes, with most of the forms cache problems fixed, and two new Junk mail options – add people you reply to to the Safe senders list and block messages by top level domain (.us, .de. .it etc) or by character set encoding.