Perhaps the biggest surprise for me was on the memory that the machines use. The new PowerMacintosh computers use 72pin, 80ns memory. While they must be installed in pairs, this RAM is slower than is needed for the current Quadra 800 and 840av (60ns), or the Centris 660AV and Quadra 660av (70ns). Essentially, if you have memory for a Macintosh LCIII or newer you can bring your SIMMs to the Power Macintosh party.
Also, if you have a GeoPort from a Quadra/Centris AV machine you could use it with a Power Macintosh. Apple has provided the software on AppleLink to use the pod with your new machine.