There's no shortage of people that have had problems with Mac OS 10.5 Leopard (including data loss, login jams, Time Machine errors, Finder weirdness and even the dreaded BSOD). Apple appears to be moving to address these bugs in a quicker-than-usual manner.
According to AppleInsider, the initial builds of 10.5.1 have over 24 bug fixes including: Firewall, Spotlight indexing, iCal syncing, Keychain login, text drawing corruption and fixes for Leopard's email client, to correct Mail syncing, HTML anchors, Email alarms, To-Do Notes, and smart mailboxes.
MacRumors adds that the update will address problems with Disk Management, DesktopServices and moving files across partitions, Text Drawing, iCal and CalDAV syncing, Read-Only Issue with SMB and AirPort 802.1X.
No timeline has been given for release of the update.