Apple has released the first update for Leopard, Mac OS X 10.5.1, with a laundry list of fixes for widely reported problems among early users. It's available via Software Update in Leopard, with the downloads under 40 MB for both PowerPC- and Intel-based Macs; oddly, the standalone versions for the desktop and server versions of Leopard weigh in at 110 MB.
One significant improvement is Apple's statement that 10.5.1 "improves the reliability of Back to My Mac-enabled Macs appearing in the Finder's Shared Sidebar." In our experience and that of colleagues, Back to My Mac has worked erratically or not at all, but early signs are promising; see "Punching a Hole for Back to My Mac" (2007-11-17).
The 10.5.1 update also reportedly fixes problems in storing wireless network passwords and using Disk Utility, and it addresses five Mail flaws. A bug that resulted in "potential data loss issue when moving files across partitions in the Finder" has been corrected; this issue cropped up when using Command-drag to move, not copy, files in the Finder across local hard drives and mounted volumes. Most other fixes are cosmetic and minor.
One missing fix in this release is a solution for the progressive Wi-Fi performance degradation experienced by some AirPort users.
The update also fixes some security and usability issues with the firewall, some of which we have previously covered (see "Leopard Firewall Takes One Step Forward, Three Steps Back," 2007-11-05). The label for the Block All option has been updated to read "Allow Only Essential Services." In other words, the firewall behavior hasn't changed, but the label now more accurately represents how the firewall functions.
The most notable other changes are in the application firewall: Skype and other applications that modify themselves when they run are no longer rendered unusable when the application firewall is selected. In 10.5.0 the application firewall would digitally sign the code of any application you authorized for network access and refuse to run the application if the application changed (a technique to protect your computer from attackers). Now, instead of just stopping the application from running without notifying the user, 10.5.1 prompts you to allow network access again if the application has been modified.
The application firewall now also enables you to block programs running under the root user, giving you much better control over your system. These don't completely fix all of the problems with Leopard's firewall, but they're good steps in the right direction.