USB systems are really a new implementation of existing technology. When working with most of these systems, you create a connection by plugging one end of a double-ended adapter into each of the two machines you want to connect. If you want to connect three machines, the machine in the center (machine 2) will have two connections: one to machine 1 and one to machine 3. This is called daisy chaining, a technique used by other networking technologies.
Some USB systems rely on an Ethernet-like block. You plug one end of the USB cable into the computer, while the other end goes into the block. These systems tend to have fewer reliability problems and transfer data slightly faster than the daisy-chained models. However, they're also more cumbersome to set up and tend to cost a little more than the daisy-chained models.
The feature that makes this solution easier than creating a full-fledged Ethernet network is that you don't need to open the machine to set up the network. Everything is taken care of by your USB port and the external adapter. A simple automated software setup completes the installation process. In most cases, the only question the installation program will need to ask is what you want to call your machine (every machine on the network has to have a unique name). One of the most popular USB connection solutions now is from Parallel Technologies.
When it comes to speed, USB systems fall short of new home phoneline systems, but can exceed the capabilities of home wiring systems. You'll find that you can get about 2 to 5 Mbps transfer rate from a USB system. The one area where USB systems shine is in a low latency time of 1 ms to 20 ms. Latency is the time required for one system to respond to a request made by another system. The latency levels for USB compare favorably with the higher rates generally experienced by both home phoneline and home wiring system users.