$10.83 ($6.99 as of 09/10/11)
If you own Rockband on Xbox then you may know that there are only 2 USB ports on the Xbox. If you wanted to have a party for Rockband playing you usually have 1 singer on the mic, 1 drummer, 1 guitarist, and 1 bass player. That totals up to four instruments that require a port.
You will need a USB Hub to use this configuration, even if one of your guitars is the new wireless technology.
I've also resorted to using this on my laptop. I've broken almost all of my USB ports on the back of my laptop. It's helped me hook up numerous things at one time that I'd have to swap out each time I want to use it.