I noticed an update waiting for me this morning on my Rogers Lumia 920 (Portico update applied a week or so ago). Not much detail as to what the update did but I managed to snag a screenshot of what little detail there was. It took a little north of 10 minutes to apply.
The KB # appears to be one of those in the Portico update so I'm guessing a fix to something from the main update but that's just a guess. I haven't seen anything that looks different but will report if I do later. Others may have keener eyes than me however!
Just checked mine on AT&T. Says my phone is up to date. The OS version on my phone matches the number in the picture, so I'm thinking that AT&T phones already received this update.