I was really close to ordering one a while ago, but started to think about the very high pricetag. Sure, I'll use it for work, and I do need CPU performance and OpenCL now and then, and I play some games now and then. But Xeon multicores, ECC memory, D700's and such are just a bit overkill for what I do, and not really worth $9k or thereabout to me, even if I really like it a lot. I also run an iMac now, and I miss the option to have separate external monitors too.
At the moment I'm leaning towards a hackintosh build. Did some research, and I can get a good looking small case, a 3.5 GHz quadcore haswell cpu (easilly overclockable to 4.5:ish, and upgradeable to broadwell when it releases very cheap), fast SSD's in a raid setup, dual 280x in Crossfire (that would match d700's for gaming / openCL) and so on, and get it for a price that's around a third of a similar MBP. Also, I like tinkering and building stuff, so it could be a fun project