Just a little wrap-up on the day that it became clear that the final build of Mac OS X 10.6 is 10A432, the version that has last been tested by developers:
1.) You can either upgrade from Leopard (with the 29$ retail disc or the 9.95$ up-to-date disc) or Tiger (with the Mac Box Set) or clean install using Disk Utility when started from the disc. All of this only works on intel Macs, but works on _all_ intel Macs.
2.) Unless you've got an Xserve, your Mac will boot the 32-bit kernel per default. Some - but not all - newer machines allow booting the 64-bit kernel, but as a general rule: You shouldn't care. If you ask yourself whether the 64-bit kernel would do any good for you, it won't.
3.) Rosetta can be installed directly from the 10.6 installer, but if you forget to install it and have an application that requires it, Software Update will download and install Rosetta for you without rebooting. You just have to start the application again yourself after Software Update finishes installing Rosetta.
4.) Quicktime X has no preferences. There basically *are no settings*! You can, however, install Quicktime 7 from within the 10.6 installer. This application still has preferences and you can add your Quicktime 7 Pro code from within the Quicktime 7 Player and have its features in 10.6.
5.) Some reports claim that the 29$ "Upgrade Disc" actually is a full disc, meaning that you don't have to have Leopard installed at installation time, and it also won't ask you for your Leopard disc. However this disc, according to the reports, does _not_ allow you to upgrade from Tiger. So there _is_ a difference between the discs. The "Upgrade Disc" allows clean installs and updates from Leopard, the Mac Box set behaves just like Leopard Retail did and lets you upgrade from Tiger and Leopard and also allows for clean installs.