While PowerBlock for Mac does stop the computer from displaying a shutting down window when you quickly press the power button, it doesn't impede the shutdown function triggered by holding down the shutdown button -- making it an app of limited use.
Upon first starting PowerBlock for Mac, a pop-up box warns you that the program could cause your system to fail -- keep that in mind. The app's main feature is to ignore quick presses of the power button and, if selected, run an AppleScript. This can be useful if you use a MacBook and happen to accidentally press the power button key more frequently, as it will completely block this button. However, pressing and holding down the shutdown button still forces an immediate shutdown, so if you want to perform a hard shutdown on your Mac, you can still do it the old-fashioned way. When it comes to looks and options, the app's interface is rudimentary at best and there are not many options to set. Checking a box for running an AppleScript lets you run a specific script that will, for instance, shut down your system immediately when the power button is pressed. You can edit this script and adjust it to your preferences, which is handy. Apart from running an AppleScript, you can set the program to start immediately after logging in, as well as to automate update checks. You also have the option to manually click a large button to check for new updates. There is also a large conspicuous button taking half of the main application window leading you to the developer's site for more programs.
If you want to completely ignore presses of the power button, or are annoyed by the confirmation box that comes up when clicking the power button on your Mac and want to get rid of it, you may want to try PowerBlock for Mac. Don't expect more from this app, though.