The size is truly important to me. Being able to pack up two of these and move them between locations and merely plug them into an already established setup elsewhere is game changing, for me.
I initially frowned when I saw the comparisons, but as others have said... Beta 1 of an OS on brand new hardware isn't exactly a deal breaker.
One processor vs two seems pretty obviously like a result of thermal issues. Two twelve core processors jamming along near 100% would not only create internal hardware issues, but it would make sitting anywhere near the thing pretty miserable.
Many applications already take advantage of GPU processing. That will only become more common... Not worried.
Any company that is really concerned with its own longevity has already invested on some level in Thunderbolt expansion and storage. That will obviously increase dramatically with these machines and TB2. The advantages are too great and outweigh the likely high costs.
Worst case scenario (for me), I have a Mac Pro with much more expansion- that I've prepared for (maybe even slightly prematurely, although our MBP users use them pretty heavily), its much more convenient to take from location to location, and based off of this single geekbench result, is faster than stock previous gen machines on increasingly insignificant statistic.
I won't modify my machines. We use AppleCare and Joint Venture and its just an asinine move for us to throw that away when the turn around times and loaner machines from Apple are excellent the majority of the time.
We choose to keep our IT staff fairly small. By investing in the solutions we have, including taking advantage of Apple's frankly outstanding services for small businesses, we can afford to do so and easily afford to adopt somewhat cutting-edge technology. I suspect other companies with a larger IT staff is spending a lot of our budget on their head count. Not saying its wrong or bad (I was an IT once upon a time! That job market has been brutal since 2001)... It's just not how we are currently operating.
I don't mind the complaints though. You saw what happened with the XBox One and Apple Maps. Opinions are important and can change things... and if it results in improvements, we'd all be glad there were passionate people out there who have needs that aren't met by the current offering.
Regardless, I believe we will see much better real world performance than many of you are expecting. The nMP will likely launch alongside updates to Final Cut Pro, and possibly even Logic Pro, which is the Mac Pro of software these days- and probably going to see a radical redesign in the same way.
TLDR: It fits my needs quite well, and is faster than my current machines which are fixed in place basically. We are invested in Apple's ecosystem for businesses, so modifying previous gen machines isn't an option. We (my partners and I) are also pretty convinced that this machine will surprise the-currently-disappointed with its hopefully stellar real-world performance (alongside optimized software updates).