When Facebook announced a change in their privacy setting and the fact, that user information would be shown on other sides, I doubt this was what they had in mind.
As techcrunch reported on their blog, there is a major security lag at Facebook. By using the feature, that lets you check how others see your profile you can actually have a look at their Chat log. The following video shows it in detail.
By now the Chat is down for maintenance.
But thats not all, raysourav found out that by using the same mask, you can click the user picture and than accept or decline friend invites. This is shown here. I could not verify if that is true. I tried it with some friends, but either they have no open friend requests or it is as well fixed by now.
19:39 edit: the second gab is closed as well. Chat back online.