If you have an order number and the expected ship date has passed, I would call. I ordered one via the web on the afternoon of the 19th. I didn't get an order number via email, so I called the next day. They said that for some reason my credit card info didn't get transferred with the rest of my order info. So, I was apparently put on a list to be called by Dell people to get the necessary info (I take it this was a common ocurrence -- odd). Well, my call straighten it out preemptively and they said it should ship by the 25th, plus I paid extra for 2 day shipping.
When I didn't receive it on the 27th, I called again. They said they didn't know why it wasn't shipped, but they expedited my order and said it should ship within 24 hours. We'll see.
I suspect that Dell is hoping that some of these orders will fall by the wayside if they let them sit long enough. I wouldn't pester Dell, but if your ship day passes and your credit card still hasn't been charged, I'd call them.
Scott