So, following up. Here's the parcel as it arrived on our doorstop. As you can see, FedEx Freight munged the outer packaging pretty severly, but the mattress itself was packaged well - inside both a vacuum seal bag (which was the most important part of it being compressed), and then further again wrapped a full 3 or 4 times in a thicker heavy duty plastic. The combination of both saved the actual mattress from any damage or dirt in the end.
It weighed just about 100 pounds...remember, king sized. Me and my son got it upstairs (still in compressed sausage form) with relative ease despite the grumblings of a 19 year old being asked to actually do anything physical.
Once we got it onto the box spring I started to unwrap the heavy plastic outer wrap - it readily started to unroll and eventually layed mostly flat...however once I cut open the vacuum bag the magic really started and it quickly expanded to near full size inside of only a few minutes. About 20 minutes later it looked like the photo below....not quite at 100% yet, but we left it for a few hours more and it had filled out 100% as the foam completely expanded.
I reassembled the bed (we took the new mattress as an opportunity to rearrange our bedroom a little) and we slept on it the same night.
I was impressed! The memory foam is very evident as I felt the mattress conforming to my body...and for the first time in a long while I work up without any aches and pains.
It's somewhere on the medium firm side I'd say - not so plush that you sink into the memory foam and can't move, but not so hard that it creates pressure points either. Reading the reviews its seems the consensus is that it's on the firm side, but some people who were obviously sleeping on something akin to a piece of plywood complained it was too soft. YMMV.
Like any new bed I think it'll take a few nights to really get used to it, but all in all....for $450 delivered from California (for a King!), well....we're happy to far. Longevity remains to be seen.