(Click to enlarge note - which was made with School Notes Pro on my iPad.)
Not a perfect solution, but it is possible for me to print images up to 5" x 7" from my iPad, via wifi printing to my HP printer.
2 key bits of information:
1. You can take a screen shot with your iPad in the same way you do it with an iPhone - briefly press the power switch and the home button at the same time. The resulting .png image turns up in your Photos application.
2. HP makes a free app called iPrint for the iPhone and iPod touch which lets you print photos to your wifi-connected HP printer. iPrint also works on the iPad.
Challenges I have not yet resolved:
While photo resolution is crisp-ish on screen shots, the .pdf files that Mail will let me save to the Photo app are fuzzy.
I can't persuade the application to let me print anything larger than 5" x 7".
Still - it was very cool to press print on the iPad this afternoon, and hear the printer in the other room rumble into action.