I did a lot of looking around, and read the customer reviews of products, which actually constituted a great discussion of how people use them differently and the pros/cons. (One person put it really well: that first and foremost, you have to decide whether you're a cover person, or a sleeve person. The cover is a bit heavier to hold, but simpler to use: you just swing it open/closed. The sleeve is slightly lighter in your bag, and lighter still (zero added weight) holding the kindle to read. It's also cheaper.
I had already decided that weight is crucial: I like to read sitting up straight because of my back issues, holding the book up high so my neck doesn't strain. It's got to be REALLY light. And every ounce in my backpack matters to me. So I went with the sleeve. (To start, at least.) The downside is putting it in/out. Ideally, I'd love to pull it out of my bag and have it ready to go on short subway rides--and not have to put it back into its sleeve--so I at least went for a really simple sleeve. I definitely don't want to be messing with a zipper. (Yes, that will keep me from pulling it out on a crowded subway on a short ride. I got a simple velcro one.
This one is supposed to arrive tomorrow:
http://www.amazon.com/gp/product/B005K2YKEU/ref=ox_ya_os_productI'll let you know how it goes.
Looks like a nice sleeve. Thing that stopped me from getting a sleeve is that I would be afraid to drop it when naked. My hands sometimes don't want to work as they should, getting numb feeling in my fingers and hands so I rather have something around it in case I do drop it. But with the Atlas Marware above which i now have used for some time, it really works nice. I can slip my fingers through the grip and that way it holds a bit more comfortable and this cover barely adds any weight as far as I can feel. From what I've used it up to now I really like it.
About the Amazon cover..I have the lighted cover for the kindle 4, basic kindle and I didn't like it. The light was okay, but the cover itself is really smooth leather, especially the back which is so smooth it becomes very slippery. I had it around my K4 for a day, but changed it back to it's previous Gecko cover because when picking up the lighted cover I just had to be really careful of not letting it slip from my hands, because it was so slippery. Also compared to the old lighted cover for the kindle 3/keyboard, it feels very flimsy, especially the front cover. Also if you want to take it with you in your backpack I wouldn't buy the amazon cover because there is no way of keeping the cover closed. no elastic like my marware cover, nor a magnetic closure. Nothing. And unless you plan to keep your reader in a seperate section of your backpack then, you stand a big chance of damaging your screen when something comes between your cover and your kindle.