alright dont take my word for this, because when I spoke to facebook about iPhone apps this was a year ago. Last I spoke to facebook, they had one guy, thats right....one guy working on their iPhone dev. I was applying for an internship and expressed my interest in the iPhone dev and they told me it was one dude. Now i've also heard facebook is considering outsourcing its iDevice dev, but until that becomes the case I would say its going to be a while before you see a full-fledged app.
Honestly, kudos to the one guy for getting the iPhone app where it is today, because thats an accomplishment on its own.