I'd say it depends on the apps you depend on (Apple's apps will probably start with a leg-up on using the new hardware better), but that buying the final generation of proven hardware is probably a safer bet than the first generation of new and drastically different hardware.
But if you're a life-long Apple guy you've faced this multiple times before... 680X0 to PowerPC, PowerPC to Intel, and now...
I wonder about the prospect of mainstream applications being as fast or even bothering to support a vastly different architecture, but then they claim it emulates/etc...
