You know the same thing happened this summer with the iPhone 3GS. Our cards got pre-authorized, then charged, then it took like 2 days before it actually showed that it shipped from the factory, then it got through customs in Alaska (yay!) and everyone was excited we'd get it three days early. Then it got to the main routing hub in Kentucky or whatever and sat for two days since Apple told them to deliver it on a certain day.
I'm sure a similar thing is happening. Everyone will get all excited that they have tracking numbers on Monday or Tuesday, hammer the FedEx/UPS site all day until it's held up at the main hub, then come here and bitch, then resign themselves to their fate that it'll be delivered on April 3rd (like Apple told you). Some people will bitch about how "if it's not delivered on April 3rd I will call and demand Apple give me 60 new Macs" or some craziness, then it'll be delivered on the morning of April 3rd and the forums will go silent as everyone plays with their new toy.
Relax. It's coming on April 3rd. Nothing unexpected going on.