Microsoft has decided to delay Software Update Services (SUS) 1.0 end-of-life until July 10, 2007. This means you have exactly 8 more 'Patch Tuesday' cycles before SUS 1.0 ceases to function. For anyone keeping track, this was supposed to be the last month patches would synchronize to SUS. Technically the EOL date was Dec. 6th, but since that's before December 'Patch Tuesday', SUS Admins would have been out of luck.
You can find the official announcements on the WSUS Product Team Blog and the SUS product page.
Seriously... can anyone come up with a reason NOT to upgrade? I realize many IT Pros are overworked and underpaid, but the upgrade from SUS 1.0 to WSUS (SUS 2.0 if you wish) is about as simple as they come in this business. And to dispel any conspiracy theories, WSUS doesn't require any additional licenses (above and beyond what's already required for SUS 1.0) or OS upgrades (WSUS runs on 2000 Server). So, to summarize... no cost... more products supported for patching... MUCH improved reporting... what are you waiting for?