The majority of All-In-Ones (AIO) for the consumer market is being built with photographic output in mind. Most of the standard performance features mentioned in the printers segment should apply here. However, because of its multifunctional ability, there're a few other points to look out for.

Scanner One of the pull factors of an AIO is actually the scanner function. Without delving too deeply into the complexities of the two main types of scanner technologies, CCD (Charge-Coupled Device) units tend to do better in terms of image quality, especially when scanning the gutter of a book. The main advantage of CIS (Contact Image Sensor) scanners is that it's much more durable. Other things to look for are sheet-fed vs. flatbed units, with the latter allowing you to scan thicker objects. Do get an OCR (Optical Character Recognition) package along with your purchase as it converts scanned pages into editable text documents, possibly saving you countless hours if you've lost the original soft copy. And if you're planning to archive your old photos, look for attachments that allow you to scan slides and films. It's also advisable to find a model with the necessary software to automatically remove scratches and dust, as well as offer some form of color restoration.
ADF (Automatic Document Feeder) Copy speeds can never be decent unless your machine sports one of these gizmos. Compared with lifting and replacing documents umpteen times, faxing and copying multiple copies can now take as little effort as a few button presses.
Fax Besides the fax connection speed, other things to look out for here are ease of use and memory storage. Having a machine that has more quick dials and number storage can also be a godsend, especially if you're not the type to keep numbers neatly in a phonebook.
Versatility Strange as this may sound, not all AIOs are capable of working as standalones. The budget units need to be tethered to a running PC, severely limiting layout and resources.