Well... I was holding out hope against all hope that Apple would be announcing a 17" MacBook Pro Retina that included a lock slot, but instead they announced a MacBook Air product refresh and a sneak peak at the MacPro.
So, I went with the 15" MacBook Pro Retina and purchased the PNY ThinkSafe Portable MacBook Locking System to secure it.
While I can't say that I'm in love with the idea of using a hinge to secure the MacBook Pro, the PNY product does the job well when it comes to locking the laptop down. I was worried about the hinge scratching the display, but it never comes into contact with the glass in a way that would allow it to scratch. I was also a little worried about losing the hinge, but it attaches easliy to my keychain when not in use. The hinge does slide around a little bit if the laptop is open when you move around, but I find that to not be as annoying as I had expected. It did take a little getting used to making sure that the hinge is positioned just right so that the laptop can close completely, but even that just took a few minutes to adjust to.
I think everyone who's posted here understands the need to be able to lock a laptop down. While the PNY solution is not as convenient as a built-in slot (what will be?), at least I'm not worried about my laptop being an easy target for a would-be thief. In no way ideal, but effective nonetheless.
I forget who originally posted a link to the PNY product in this discussion threat, but thank you.
-Warren