Old-style plist parser: missing semicolon in dictionary

I've noticed this message (with a few variations) in the console. It pops up probably a few hundred times a day.

CFPropertyListCreateFromXMLData(): Old-style plist parser: missing semicolon in dictionary.

The reporting applications include:

System Preferences
Safari
quicklookd
Mail
iTunes
LaunchBar
Google Earth
(just from the past few hours)

I ran Preferential Treatment which found no problems with either my user nor my system preferences.

I'm not sure whether this is affecting system performance overall, but it is strange and if anyone has a clue about what I can do to stop this from happening, I'd be glad to hear it!

Thanks,

Dave