I bought the lighted book cover from Sony for my PRS-600 reader. In my opinion, the case is NOT worth the money - not even if you can get it on discount. I love the convenience of having my light always with me, because I always use my light. However, the Sony lighted case, even on the high setting, didn't produce enough light to see. I always found myself wishing my old Sony lightwedge case for the 505 would work with the 600, but it wouldn't.
However, I have found something that I LOVE and that works wonderfully. Check out
M-Edge cases and their e-Luminator lights for the Sony PRS-600.