Why anyone would pay 10$ for a 3rd party solution, let alone be stupid enough to buy a new HP printer for AirPrint to work, defies common sense.
Follow the instructions here:
http://blog.steventroughtonsmith.com/2010/11/return-airprint-sharing-to-mac-os-x .html
and in less than two minutes, including reboot, you can re-enable that functionality that was disabled during beta testing of iOS 4.2, with
every printer.
I did it for all my 'puters and printers, and it's just so silly, because it works. FYI I have a Samsung laser printer, and a lame HP color jet thingy.
They (Apple and printer businesses) don't want you to use this, or even know about this, because printer businesses probably threatened to sue Apple for software patent infringement (i.e., those stupid printer drivers, a technology that should have vanished aeons ago).
But it is not illegal to tweak it yourself, nor is it going to damage your OS X. Heck, if anyone's paranoid about that, jsut backup the old files... all three of them, adding to about 10-15 seconds to the suggested workflow above...
If someone's not tech savvy, do be aware that accessing /usr/share and /usr/libexec is easier from Finder, but smoother from Terminal, as it may be the case that the permissions associated with those hidden system folders exclude the user attempting to copy and paste files to them. If this happens, login as an admin, and if OS X still won't have you overwrite the files, right-click on the folder from Finder, select "Get Info", then at the bottom of the info window, click on the little lock icon under Sharing and Permissions, and add yourself to the list as a user with read & write privileges...
Reboot, re-add your printer through System Preferences as per instructions on the website, and enjoy AirPrint right away from your iPad, iPhone, or iPod Touch...
Peace out
Herr Doktor Sly