Working with USB printers. Both the Network Edition and Home Edition support USB printers, but in different ways. Unlike the Network Edition, the Home Edition lets you connect a USB printer directly to the xPrintServer or through a USB hub attached to it, which lets the xPrintServer autodetect and set up the printer for you. Both xPrintServer models support USB printers attached to routers on the network (that is, routers that have a USB port and built-in print servers, as many do today). However, you must go to the xPrintServer's Web console and manually add them in its administration pane. You need to know the printer name and model and its IP address for xPrintServer to AirPrint-enable them.
A side benefit of attaching a USB printer directly to the xPrintServer Home Edition: It makes that printer available not just to your iOS devices but also to your Macs and Windows PCs. OS X Lion and OS X Mountain Lion support AirPrint natively, so they'll see any USB printers attached to your xPrintServer in the Print & Scan system preference when you click the + icon button to add printers. On Windows, it's not so easy; Windows XP through 8 do not support AirPrint or its underlying Bonjour networking protocol, so Windows' native network printer detection will not see AirPrint printers. But Apple has a free utility  that solves this problem, detecting and installing AirPrint printers in Windows.
Limitations in the xPrintServer line. The one significant limitation to xPrintServer is its scale. It's really designed for small office and departmental networks, with one device plugged into each LAN segment. Each xPrintServer is individually managed, so an IT organization encompassing multiple LAN segments and locations that wants to centrally manage them needs to look at an enterprise-oriented server instead -- meaning EFI's PrintMe Mobile software for Windows.
My one wishlist for the xPrintServer is that it would work over Wi-Fi relay. It now requires an open Ethernet jack on your network where it can be plugged in. That's usually no big deal in a medium-size or larger company's office setting, but it can be problematic in a small office relying on consumer-grade routers that almost always come with just four (or fewer) wired Ethernet ports. They can fill up fast, leading to awkward daisy-chaining of slave routers.
Still, the xPrintServer is by far the easiest way to AirPrint-enable your printers. Unlike the applications that convert your Mac or PC into an AirPrint server, the xPrintServer works whether or not your computers are on. That way, you can print that boarding pass at 4 a.m. from your iPhone at home, without first starting up your computer.