USB Cable Length Limitations:
The USB specification limits the length of a cable between full speed (or high speed) devices to 5 meters (16 feet 5 inches) and for low speed devices the limit is 3 meters (9 feet 10 inches). This means you can't just connect a bunch of extension cable together and run them 30 feet to another room but you can say connect a 6 foot and 10 foot cable for a total of 16 feet.
Most USB products are full speed (or high speed USB 2.0) and have the 5 meter limit. Low speed devices are generally keyboards and mice. If you would like more information on the technical side of USB you can search the internet for information on the USB specification (sorry eBay does not allow links in guides otherwise I would include one).
In order to go beyond these limits you need to use USB hubs, USB active extension cables or USB over Ethernet products.
You can use extension cables and up to 5 USB hubs connected together to extend USB's range up to 30 meters (up to 27 meters for low speed devices). The distance between each hub can be no more than 5 meters.
Active Extension Cables:
USB active extension cables contain electronics which regenerate the USB signal. These cables are essentially 1 port USB hubs and will allow you to go up to 30 meters (up to 27 meters for low speed devices) buy connecting up to five active extension cables together (4 cables if you are connected to a USB hub). .
USB Over Ethernet:
There are USB Over Ethernet hubs but I was to find very little documentation or other information on them that was useful. What did stand out about these devices is that they are hard to find, expensive and you are still generally limited to a maximum of 30 meters.