If an application is playing up, it may be due to a corrupted preference file.
You can use the built-in command ‘plutil’ to verify any preference file – for example:
$ plutil -lint ~/Library/Preferences/com.apple.iChat.plist
/Users/waffleblog/Library/Preferences/com.apple.iChat.plist: OK
Please note that this utility will only check the syntax of the file, not the deeper meaning as understood by the owning application.
To check all preferences in your Library folder:
$ find ~/Library/Preferences -name “*.plist” -print0 | xargs -n1 -0 plutil -lint
(This uses -print0 and -0 to cope with spaces in filenames.)