An open mind works both ways. People have pre-ordered it and having even see the picture quality yet. Some people are already ripping DVD's in preparation of the Appletv. Doesn't seem like open mind to me.
The lesson in compatibility is wonderful, but unfortunately my experience with a couple of updates (Airport and Quicktime) just doesn't make me very optimistic that everything will continue to work. I'll hold off for a while, thank you.
I installed Quicktime 7.1.3 update and it broke my Casion EXLIM component. Installed Airport update and computer doesn't find wireless connection waking from sleep. If Apple's own apps won't work on a OS one major version prior to leopard, I would be pleasantly surprised if my apps continue to work on the OS with such a big change. I definitely wouldn't rush to upgrade because everything works for me with OS 10.4 now.
It sounds scary that Apple's applications would be Leopard only. That would mean the OS has changed a lot and most of my current applications might break. I would definitely wait a lot longer before upgrading.