Well, since this is way out of my realm of expertise (and interest), I was going to stay out of it, but since i've been provoked...
I wholeheartedly favor Todd's definition over Talli's. After all, he enumerated 9 planks, compared to Talli's 7. Even adding that "mission critical" piece only gets you to 8. Also, reason #7 doesn't count since it defines "enterprise-class" in terms of itself. Too recursive.
I also like the fact that Todd's enterprise class system can be implemented with "a linux box, Rolf, and a nearby pizza place".
