This may go down in recent technological history as one of the most disorganized, ham-handed launches (even though it's ONLY pre-orders, the fact remains that they have had AT LEAST a week to prepare for this).
Apple was still taking pre-orders for the 3GS days before the launch date. Its always hard to judge the demand though because to anyone on an iPhone forum, everyone is getting an iPhone 4. Realistically I would think you could still pre-order for at least a couple more days and be good. Its anyones guess.
I don't know. Shipping dates for Pre Orders are slipping in the UK already to the 2nd July. Not to mention Reserving the 32GB model is pretty much out aswell