In Ted Landau's recently published column regarding .plist files (and specifically their tendency to become corrupt), it was noted that the cause of damage to these files is generally the result of a problematic write to their data. The causes for these problematic writes are varied, but it is important to note that the host application -- for which the .plist file is named -- may not be the only application writing to that file.
Take for instance the com.apple.Safari.plist, which is one of the property list files most prone to corruption under current iterations of Mac OS X. It could be reasonably assumed the Safari is the only application that writes to or reads data from this file. However, this is not the case. Other applications, including Mail.app and some third-party programs, manipulate this file.
As noted by MacFixIt reader MC:
"I've noticed that applications other than Safari are writing to com.apple.Safari.plist. Normally, I keep it locked so that my browser window size and position are maintained. However, when I open Mail.app and modify something in the preferences and then close the prefs window, I get an error message saying that I was unable to save my prefs. As a matter of fact, my Mail preferences were saved. It's just that it couldn't write to com.apple.Safari.plist instead.
"So I unlocked the Safari.plist file and did a Get Info on it. When I launch and quit Mail.app, my Safari Get Info window closes, indicating it's been modified. Other apps are writing to Safari.plist as well, like System Preferences or even a third-party app, such as MPlayer OSX. When I quit MPlayer, it gives me an error message similar to what I got from Mail.app. Only by unlocking Safari.plist and opening another app to save to it does the problem go away."
Understanding that third-party applications are able to, and routinely do modify property list (.plist) files makes it easier to recognize why these files routinely become corrupt thanks to potentially buggy write routines in said applications.
So if you are experiencing repeated corruption of the com.apple.Safari.plist file or another .plist file (see this tutorial for an example of an issue caused by a corrupt com.apple.Safari.plist file), you may want to investigate other applications that could be writing to the file.
This can be accomplished by navigating to the com.apple.Safari.plist (or other) file in the Finder (it's located in ~/Library/Preferences), then selecting its icon and going to "Get Info" under the "File" menu. Next, use some of your routine applications and check for the "Get Info" window to close, indicating that the .plist file has been modified. You can then identify which applications are modifying the file, and determine whether or not they are causing corruption.