I have the lighted cover for my Kindle Keyboard and as far as lighting up the display goes, I think that it does a good job even though the light source is on the corner. I have only two complaints about it. The first has pretty much nothing to do with the cover directly, but I prefer to hold devices without covers, so obviously I can't do that if I want the light. The second complaint is that since the light shines down and to the left, there's a very narrow angle at which the light will shine onto whatever's on your left side, such as onto whoever's sleeping on your left in bed. You can use the front of the cover to block the light, but obviously it's not ideal. If you don't mind reading with a cover on and if this shining light onto whatever's on your left isn't a big deal, then I completely recommend the lighted cover. The quality's great and I've had no problems with the contacts (I think that only early lighted covers had this problem).
Edit: I see that I took too long in typing and the "light on the left" thing has already been addressed.