OS X: Application won’t open; not allowed to exec quarantined

In OS X 10.8 Mountain Lion, the new Gatekeeper feature has a mechanism that prevents certain things from opening.  This is only apparent if you run Console and observe the error message that appears when you attempt to run an application that it shuts down:

5/11/12 9:44:57.000 AM kernel[0]: qtn-exec: not allowed to exec quarantined /Applications/Arq.app/Contents/MacOS/Arq: 00000047

An FAQ entry about this issue appears on an application CodeKit site:

Did you unzip it using a third-party unarchiver such as an app downloaded from the Mac App Store? OS X automatically quarantines all items that are unzipped without using OS X’s built-in archive utility.

[...]

You can resolve this two ways. First, delete the app, re-download it, and then unzip it using OS X’s built-in archiver app. Alternately, you can follow the instructions found in this GitHub thread. If you’d like more information about the archive/quarantine issue, see this Apple Discussions Thread. (Long story short: it’s one more bug in Apple’s poorly-implemented and oft-delayed sandboxing initiative.)

The current state of things is that there is no UI for removing this quarantine tag when the item was unarchived using a third-party tool like recent versions of the popular tool, The Unarchiver.  It’s a bug with the current OS X implementation.  One must resort to using command line tools to remove the extended attribute.  You, like me, might be very comfortable with this idea, so here’s a one-liner to recursively remove the flag on an item:

xattr -dr com.apple.quarantine /path/to/folder/or/application.app/

Ideally, this post should be obsoleted within a month, but it has caused me more grief in one week than I could handle with only two bottles of Code Red Mountain Dew.