Apple's annual developer conference in San Francisco.
Apple Seeds Mac OS X 10.5.1 9B13 to Developers
Apple details a number of issues addressed in the seed. Specifically, there have been fixes to Mail Sync, Spotlight Index, Disk Management, DesktopServices and moving files across partitions, Text Drawing, iCal and CalDAV syncing, Keychain login, Read-Only Issue with SMB, AirPort 802.1X, Application Firewall, To-Do Notes, and Smart Mailboxes. This list of issues, however, is never exhaustive, so other bugs may have also been addressed in this seed. The seed is only available to ADC developers, and not yet available to the general public.
Apple released Mac OS X Leopard on October 26th and sold over 2 million copies in the first weekend. There have been some vocal complaints about bugs in the first version of Mac OS X 10.5.