Hi,
I think one of the biggest negative factors will be their price. But Mac Pros were always expensive, and cost more than similar spec'd PCs.
The new Mac Pro when nicely souped up with memory, and external TB2 peripherals, PCI expansion Chasis, ...etc. will cost a bundle !
The cost factor will be its biggest negative factor, I also don't get the small size factor of the design, most deskop users don't need to be mobile, so why make it so small, and have us connect most of the expansions/TB2 peripherals externally ? which are going to consume more space anyways.
Having said so, I'm very happy that Apple decided to make a new Mac Pro ! There was a lot of buzz earlier in the year that they might be killing the entire Mac Pro line. So.. now we know that's not true. I think the new design is pretty innovative, although it could be mistaken for a trash bin [:D] I still like it. I just wish it was taller, and bigger to accomodate more expansions internally.
I will evaluate the new Mac Pro when it begins shipping, and gets more realistic user reviews of how they behave under pressure , do they stay cool, and are they super-quiet in a studio environment ? I also feel they are more geared for Graphics/Video professionals, given the dual-graphics processors.
Cheers,
Muziksculp