Well that was fast. Snow Leopard owners can run Software Update now to get the first update to the new OS:

• About the Mac OS X v10.6.1 Update
• Mac OS X v10.6.1 Update Download
• TidBITS’s Semi-whimsical Take on 10.6.1 (Haiku Included)

Looks like it’s a handful of fixes including an updated version of Adobe’s Flash plug-in and a possibly significant fix to sending messages in Mail.