Cache files exist for both the system (in the /Library/Caches folder at the root level of a start-up drive) and for each user (in the same location inside each user's home folder). Since cache files are not used to store application preferences or general settings, you can safely delete them without losing any data, and they will be regenerated as needed.
5. Verify and delete preferences files
Another common cause of application crashes and other problems is corrupted preferences files. These are the files that system components and applications use to store settings. In Mac OS X, preferences files are stored as XML property list (.plist) files. You can verify whether a preference file is corrupt by using JNSoftware's Preferential Treatment (donationware), a graphical interface to the plutil command available in Terminal.
Although this tool doesn't know what data should be in a property list file or exactly what the various sections (known as keys ) relate to in terms of the settings available to a given application, it can verify whether the data is packaged in the correct format and is readable.
It doesn't always work perfectly, and in some cases, it might report a file damaged when it isn't, but it's pretty good most of the time. By using it to verify your preferences files, you can detect corrupted files and delete them before the problem becomes bigger -- although doing so will result in a loss of settings for the affected application.
One lesser-known feature of Leopard is that it has some built-in capability for responding to corrupted preferences files. If an application crashes repeatedly at launch, Leopard will ask if you want to open the application without using the existing (and potentially damaged) preferences file for it. If you say yes and the application launches and runs cleanly, you can delete the preferences file. If it continues to crash, there's likely another cause.
Although this automates troubleshooting application crashes caused by corrupt preferences files, it does mean that applications have to experience severe enough problems that they can't even launch in order to trigger the feature. Verifying your preferences with Preferential Treatment every couple of months (or more frequently if you are experiencing application crashes) can prevent things from reaching that stage.