Um, isn't the "Labs" area specifically for Not Ready For Prime Time features? Good way to cover themselves.
Now, is anyone the teeniest bit uneasy about the fact that when something is "roboted", the preview shows nothing, as you'd expect ... but the "site" side shows exactly what a human would see, meaning that the googlebot blithely stepped in and got it?
Matter of fact, it's not really "site" on the left and "preview" on the right: it's the Google Web Preview robot on the left and the ordinary Googlebot on the right. I tried a page from a directory that's not only roboted, but has GWP locked out at the htaccess level. The left side showed the 403 page, which only the GWP robot would get; the right side showed a blank. With a page that's roboted but not htaccess-blocked, the left ("site") side shows the actual page, while the right ("preview") side is blank.
And honestly, GWP, it wouldn't kill you to include non-ASCII characters in your displayed text. Kinda blows the point of some of my pages :P