I think I believe Newegg. I never pre-ordered a product from them, but usually when I buy a product it takes a few days for it to go through (there's a bit slow in charging sometime..especially if the product is > $500 since it results in the bank having to call you to verify that you placed the order). But the invoice for say the laptop my girlfriend purchased using my account (she paid for it with her credit card).

The only date on the invoice is "Submitted:
9/18/2009 5:01:01 PM"

And I can tell you that's not the date that we placed the order, it's the date they charged the credit card. So if preorders are handled the same way then people who bought the n900 will be eligible for the rebate.