Vincent Danen advises taking a little time to clean up your old apps and make sure you have a solid backup before upgrading to Snow Leopard.
Now that OS X 10.6 (Snow Leopard) has arrived, and you've had a chance to see some of the reviews roll in, there are a few things you may want to square away before jumping on the upgrade. Some of these things include having a good backup that you can easily restore from, examining your currently-installed software to see what is still relevant, and deciding whether to upgrade or do a fresh install.
The first and most important thing is a good, quickly-restorable backup. If you find 10.6 to be rough around the edges or just plain old bad, you'll want to have planned for a quick escape back to your pre-10.6 upgrade. Time Capsule is pretty good, but it isn't the easiest thing to test a full restore of and I have heard too many stories that make me hesitant to rely on it for more than a snapshot-in-time. For serious backups, I use ShirtPocket's excellent SuperDuper! backup application. I can highly recommend it for two reasons: the support is absolutely fantastic with human response being quick and helpful, and secondly because it has saved my bacon a few times. I first bought my license five years ago for under $30USD; a light investment for such a reliable backup utility.
SuperDuper! creates a full, bootable backup of a drive. Since 10.6 is an Intel-only update, we'll just look at Intel support. First, you need an external drive (or a second internal drive). This drive must be partitioned with the GUID partition map; if it is partitioned any other way OS X will not be able to boot from it (rendering our bootable backup useless for booting). Once you have partitioned it, point SuperDuper! to the source (current) drive to do a full copy to the external drive and let it go. Once it is done, head over to System Preferences, choose Startup Disk, and you should see the external drive as a bootable choice. To verify the backup, select it from the list and reboot into it.
Once you have verified that the backup boots properly and contains all of your data, it's time to explore the applications you have installed. When I went back and looked at my list of must-haves from when I upgraded 10.4 to 10.5, I realized that about 60 percent of what were must-haves two years ago had turned into applications that I no longer use. This is due either to finding better apps or finding improved apps that combine the functionality of some of the old ones. But did I ever delete or uninstall them? Not always.
A new version upgrade is a great time to do some pruning and house-cleaning. My new list reflects the software that I want to reinstall and carry over. This will help when I do the reinstall by letting me know ahead-of-time what I want to keep.
It may also be a good idea, if you use tools like AppZapper, TinkerTool System, or Hazel, to delete the applications you no longer use. If you delete them before the upgrade, these tools will remove old preference and data files. If you don't have the app installed, there is usually no point in keeping the associated data.
Upgrade or fresh install?
Finally, the million-dollar question: Do you do an erase and install, an archive and install, or an upgrade? I tend to shy away from upgrades; I like the idea of a fresh system. After all, it was initially installed two years ago and a lot of data has been moved around, installed, uninstalled, left behind, etc. New versions are when I do all the house-keeping I should probably have been doing routinely throughout.
Archive and install is a good option; it tucks away a copy of the existing system before installing the new one fresh and it can also restore user and network settings that were configured before. This is probably the best option for most people as it retains all of your data, but gives you a fresh install.
The erase and install is my upgrade option of choice. This gives me a clean filesystem, freshly formatted and pristine. Then I reinstall only and exactly what I want -- preference files, applications, data, etc. This sounds scarier than it really is; with a bootable backup on an external/second drive, you can use the Mac Migration Assistant to restore user data and whatnot off the backup drive.
The bottom line is that a new version of any OS is a great time to do some "spring cleaning", and with OS X it is no different. You do have a lot of options in how you go about it, but the really important thing to deal with prior to any upgrade is the backup. Make sure you have one that works, is current (refresh it just prior to the upgrade), and make sure you can (and have!) tested how usable it is before you rely on it.
Vincent Danen works on the Red Hat Security Response Team and lives in Canada. He has been writing about and developing on Linux for over 10 years and is a veteran Mac user.