I started a new blog and though writing about using twenty-year-old printers from your iPhone would be a good early post
I love it! I have my printer hooked up to my network with an Raspberry Pi and would be glad to make it easier to print from the iPad.
A little party trick -- depending on the printer, you might be able to get an "in line" power tap/Y splitter for the power cord to run the Pi and the printer off the same outlet. (My printer takes a normal C14, so I just split and slapped a USB brick on the other end.)