Apple supposedly included some updates to the X11 system in the 10.5.2 update, but it is very difficult to figure out exactly what they did from their posted technical notes. A key issue that may cause some problems is that from 10.4 to 10.5 (Tiger to Leopard), Apple migrated from XFree86 (X11R6) to Xorg (X11R7). From my understanding, this is what caused some of the significant transition issues. In the long term, the Xorg distribution will be more stable and more similar to the current RedHat, Debian, and other Linux distributions. However, I'm holding off upgrading a number of machines to 10.5 until I see an official AFNI binary to be safe.