This truly is an amazing little piece of software. Especially useful for people who don't want to download Xcode (which is more than a gigabyte in compressed form), this product is far more useful than Apple's Property List Editor, as it show items in Binary (Standard Plist), ASCII, and XML formats. It only has competition from the freeware program Pref Setter, an application which seemingly lost support in 2008. While Pref Setter has a more "user-intuitive" interface, it is lacking in real features, such as changing the format.
In a nutshell, if you like your tools to be weak, obsolete, but nice-looking, sure, keep your money and use Pref Setter. However, if you're looking for something more powerful that is getting updates more regularly, pitch in the towel and buy PlistEditPro. For $30 USD, it's a really good buy.
I am aware that the last update for PlistEditPro was Halloween of 2009, but the developer, Brian Webster, delivered an update for another one of his applications this past November. Another feature that I failed to mention earlier is that PlistEditPro has AppleScript support. This is very useful for parsing a .plist file, except it is possible to use System Events to accomplish the same task.