The Express continues to have a unique option in the Wi-Fi base station line-up, which is a dual-function analog and digital optical (Toslink) port which lets it be a target for AirPlay audio streaming from iTunes on a Mac or Windows system and from any capable app in iOS. (Rogue Amoeba's Airfoil extends AirPlay streaming to any audio output in Mac OS X or under Windows.)
Previous models had an integral two-prong power plug (in 110-volt countries) that allowed them to hang directly off a wall outlet or fit into a power strip. The base station was heavy enough that it could easily fall off the outlet, and locating it by an outlet or a power strip could often mean that signals were blocked by furniture. A separate cord with a three-prong plug was only available as part of a $39 A/V kit. The 2012 Express (in the U.S. edition at least) has a 6.5-foot (200 cm) long two-prong cable that allows it to be more easily placed. It's also attractive enough, unlike the unit it replaced, to sit on top of a TV cabinet or table.
The 2012 Express, just like the two preceding models, can only share a single USB printer using Bonjour. The Extreme and Time Capsule use Bonjour sharing for a printer or hard drive (via AFP and Samba) through a USB port, but also allow the use of a USB hub to share multiple devices.
Macworld's buying advice
The quibbles about USB and ethernet are relatively minor compared to the features available in this mighty mite. For the money, the Express makes an effective base station for modestly sized apartments or homes, or where access is only needed in a few adjacent rooms in an office. This sleek model is the right choice for many, and at $80 less than the AirPort Extreme, a prudent one as well.
Glenn Fleishman, a senior contributor to Macworld, wrote a book about using Wi-Fi with Apple hardware called "Take Control of Your 802.11n AirPort Network." The third edition is updated for Lion, AirPort Utility 6, and the iOS AirPort Utility app.