The promise of iOS 4.2 for the iPad has largely been fulfilled, yet there are still gaps remaining. The ability to print to any printer via AirPrint has yet to materialize, and until Apple releases another update there is only a select (read: infinitesimally small) number of HP printers that will work.

Don’t despair. As usual, an enterprising third-party application developer has solved a seemingly insurmountable problem. That solution is Printopia, a small addition to the preference panel in OSX (it works even with 10.5) that allows you to print to any printer connected to your Mac. Not only that, Printopia also serves as a virtual printer, allowing you to save your files as PDFs or JPGs directly to your Dropbox or to your Mac.

I’m currently trying out the 7 day demo (after that, the software costs $9.95 – a meager sum to print from your iPad TODAY instead of some unknown time in the foreseeable future) and can attest that Printopia works as advertised, even exceeding my expectations in its simplicity and ease of use. Once installed, all you have to do is pull up the print menu (note that the app has to be compatible with iOS 4.2 and have a print menu enabled) and your printer will appear. No, it isn’t realizing the promise of driverless printing – yet – but it’s better than any other stopgap measure I could imagine.

A few caveats: first, you need a Mac for this (sorry Windows users), and second, your Mac has to be running in order for you to access printer resources (this includes saving to your Dropbox account or your Mac as well). Still, it’s simple, elegant and affordable. It just works.

Read more about Printopia and download the demo here.