Yes, I have three wifi networked printers.
The first is a Kodak eps9. It's a good printer but I can only use it when the pc is on with the aid of a third party app.
The second is a Brother that prints and scans in an11 by 17 inches size for technical drawings. I've used the Brother app a few times but all it prints is pictures. The app only scans in 8 1/2 by 11 but it allows to save the document in PDF and also mail the scan or save in jpeg to photos.
The most useful with the iPad is the HP D110a. Everyone knows by now that this printer is given an email address and that is how you send it documents. Be aware that it recognizes Microsoft formats such as Word, Excel, Outlook and PowerPoint and common txt files jpegs and PDFs. The rest such as Photoshop or Autocad's DXF, it refuses to print. I'd like to point out that pictures are printed only in 5 by 7 directly in the top left corner with no bleeding. I use it directly on the network via PrintMagicHD and Print apps. This is the best way to use it with the iPad, so far. It also has a flimsy carry bag if you need to take it out for a study evening with buddies.
PrintMagicHD's best feature allows to print through a pasteboard.
Print's best feature is to print web pages directly from an address, it's got its own web browser. It will not print from secured sites similar to banking pages.
My favorite for iPad? The HP.
Overall photograph quality? The Kodak.
For business? The Brother, it's the quickest and scanning 11 by 17 is just magic. But not that great with an iPad so far...oh, it's also HUGE.