Barnes & Noble gave some sense of what Nook is worth to the company in reporting fourth quarter earnings (and forward guidance for fiscal 2011). BN.com sales–where Nook units and ebooks are both recorded–rose by about $44 million in the quarter, at $141 million overall up 51 percent from a year ago. And for 2011, the company expects BN.com sales to rise “approximately 75 percent to $1 billion.” So they expect to gain another $425 million in the year ahead from Nook device and ebook unit sales. (Note that for comparison purposes, their sales estimate “reflects the actual retail selling […]