Loving mine
I've had mine 10 days, and I'm loving it. I installed 16GB of RAM and an Intel 180GB SSD along the stock 500GB HDD.
When I rebooted from an external hard drive with a cloned copy of my OS X installation, Disk Utility decided that my SSD + HDD combo was a damaged Fusion Drive and offered to auto-repair it into a Fusion Drive for me. I didn't even have to jump through the diskutil corestorage Terminal hoops that I expected to.
(On the down side, I do not look forward to having to take the SSD back out if I ever need hardware warranty service.)