I jailbroke my iPod 4g with Redsn0w 0.9.10b3 and it worked without a hitch. Although, I had been growing increasingly annoyed with the speed of my iPod, as jailbreaking significantly reduces its speed. I attempted to restore it with iTunes but "an unknown error occurred (21)" and put my iPod into recovery mode, or something of the sort (a plug with an arrow pointing to an iTunes icon). I have been tooling around with it for a couple of days now and can't seem to find a solution. Please help, thank-you.