I also have a MacPro and a Seiki 4K (39" version) and it works great and is beautiful!
I have had a number of occassions where the screen wouldn't reconnect after my MacPro went to sleep.
I am hoping Seiki will have a firmware fix for this soon!
I've actually being using 4K displays at my work for about 4 years already and have been stunned at how quickly prices have dropped from the $30000.00 we paid for Toshiba 4K displays, which we had to drive with 2 dual link DVI inputs and they were just monitors with no TV tuners, ...
I am contemplating getting a Seiki 55" for use as my TV and display, but I _REALLY_ would prefer to have passive 3D as well. Ie, I would love to get the LG 55" or 60" passive/polarized 3D display, but that is a LOT more money than I have.
Seiki, please make passive (circular polarized) 3D versions of your displays!! :-)
Better yet, LG, Toshiba, Sony, Samsung et al, please drop your prices on your 4K 3D displays!!!