It's really not possible to launch something like this well: the app is progressively launching across the globe as the update propagates through the iTunes servers. There's no specific moment where it's available everywhere, it's a roll-out process that that Apple warns you can take up to a day.
I read that Apple and Facebook were planning on announcing the app and possibly other things at the iPhone event last week but that Apple "went dark" after learning of Steve Job's health over the weekend.
If that's the case a soft, muted launch would be more understandable especially considering direct competitor Samsung/Google postponed their launch indefinitely.
Don't announce it and provide a link to it til you check that the link actually works, Zuck!
Sheesh.