I got my e-mail notice about the device shipping in late April (same as posted by others) and it has corresponded with a hold for the charges on my credit card.
When I ordered the case from apple, the hold from charges hit on a Friday, I got the shipping notice on Monday, and the product arrived on a Thursday. So the whole cycle took place over 7 calendar days, with a Sunday in the middle. That was with Standard Shipping.
Based on this logic, my 3G would be slated to arrive on a Sunday, which would actually fall to the following Monday. However I have priority shipping now, so the expected date must be before the coming Monday. At the latest, that marks April 24th, a Saturday, and possibly sooner -- although I'm not holding my breath.
Good times await! I've got 100 apps just waiting to get loaded!