For those still looking for a relatively slim sleeve for the 15" MBPr, I have now tried two cases.
The first is the Level8 15" WORLD Pro Super Sleeve for MacBook Pro/MacBook Pro with Retina Display
http://store.apple.com/us/product/H...=15inchmacbookproretinadisplay&fh=36c2%2B2c15
This case is clearly suited for the 15" MBPr, it fits perfectly. It's a different kind of sleeve than I'm used to because of the patterned interior, so that only a small amount of the interior is actually in contact with the case. The material inside isn't the softest, but I don't think it will scratch the computer. In addition, there is enough room, as well as some piping around the zipper, that makes me think the zipper won't scratch the computer. It seems well-made, but the seams aren't quite perfect (I'm being picky here), and the materials feel very utilitarian, not all that premium. The MBPr charger seems to fit in the front pocket, and it seems like it's not putting undue pressure on the computer itself in this configuration.
I also tried the Incase Protective Sleeve Deluxe (
http://goincase.com/shop/incase-protective-sleeve-deluxe-for-macbook-pro-15). This case feels higher quality than the Level8 sleeve due to the materials used, the seams are all very well done, and the inside feels much softer and perhaps more scratch-proof. However, as I said previously, this one seems like it'd also fit the 15" classic MacBook Pro, so it's not super form-fitted (though much better than the Neoprene Sleeve, for example). Unfortunately the one I ended up with had a defective zipper on the front pocket, so that won't close.
I am going to stick with the Level8, mainly because it seems like it'll protect it about as well as the Incase, it seems to be a better fit, and the Incase I got had a defective zipper.
If anyone has questions about these two cases, I'm happy to answer!