Ved,
Thanks for the pat on the back. We try for a 'bigger' release every quarter, and this is definitely it... glad some of our users are already playing around
As for that setting, Facebook renamed it on August 1st. You now should look for "signed_request for Canvas:" and make sure that that is enabled. We updated the configuration guide as well.
With that said, the Page Tab & Canvas guide doesn't talk about the Canvas stuff at all (yet), only Page Tab integration... and it's still a little rough around the edges.. so definitely let us know any issues you run into. We'll be cleaning things up as we learn where people are getting confused, but hopefully, it won't be too painful in the process!
Thanks,
Alex