There was a report that Macs shipped before 3 November would come with Tiger and a drop-in disc for Leopard. Macs shipped from Apple after 3 November would come with Leopard pre-installed.
FYI, I just had a few minutes on my lunch break and called Apple. The person I spoke to said iMacs ordered directly from Apple are now shipping with Leopard pre-installed. I don't know how confident I am in the statement and I'm still looking for confirmation from someone saying that they got a computer with Leopard on it. But atleast it's nice to hear after a week and a half since Leopard has been out.