This is so cool just because it works better than Apple’s own AirPrint option for iPhone, iPad, and iPod touch. From Mac360:
You won’t need to sync up your iDevice to your Mac. But you will need to be on the same home or office wireless network, of course. If your Mac has a printer connected to it, Printopia can find it, and your iDevice can print to it.
It just works. But not all apps are printer ready.