I would HIGHLY suggest you buy it from Google or some other REPUTABLE source.
I have hard of horror stories where people buy them "new" or used form ebay and other sources and get ripped off because the seller will call in later and report it lost or stolen or something like that.
One thing to keep in mind, that I found frustrating (because I have no patience):
I ordered mine super early one morning, and never received tracking info by late that day. I called the support line and the guy told me, "Hopefully it will ship tomorrow..." -- making it 2 days from time of order to having it in my hands. So even though you get "free FedEx overnight shipping", it isn't "overnighted" to you until they actually ship it.
Mine shipped the next day, as he said, so two days from time of order and I had it.
Congrats on the new phone! I ordered mine last Friday morning, and it was at my door in Albuquerque Monday afternoon. (Thanks to the weekend, FedEx opted to fly it from IND and then drive it here from MEM.)
I've had great fun this past week learning what the Nexus One can do -- and I haven't been disappointed yet!