I got my 27-inch BTO iMac yesterday, 11/22, ordered only eight days earlier on 11/14.
And it came with Mavericks installed.
Now, in starting to use Mavericks, I saw that it is not -- yet at least -- compatible with several things important to me: work VPN connections, using it to screen share with my music-only Mac Mini in another room, my long-time-use macro utility, et cetera.
So what I did with the internal 1TB SSD is partition it nearly immediately, half and half partitions.
And then I installed Mountain Lion in the new, second partition.
That's what I'll work with for now, and let's see how Mavericks evolves. And having a dual-boot internal drive can just be useful.
Meanwhile, I have several external HDDs attached, and that takes care of my main storage -- music, photographs, videos, and other documents. Hey, the price of good quality external HDDs is cheap nowadays -- I'm happy with Western Digital -- and that gives me all the redundancy (aka, backups) that I need.
And then, when Other World Computing comes out with their new Thunderbolt drive, I'll get the 4TB version, set it up as RAID 1 for automatic mirrored backups, and use that for my 1500-plus music albums.
Dave, who says this new iMac was "assembled in the USA"