Can anyone here who has actually used the official case comment on it?
That's likely only to be Nokia employees as I don't think anyone has ever seen it available in the wild, although there were a few sightings of "the case" at CES back in January.
I'm waiting for confirmation from Expansys that they really, really will have it in stock this time in which case I'll order one.
I have no comment on the "genuine" N800 case, but I bought this case (http://www.expansys.com/p.aspx?i=105191) several months ago at Expansys. It was recommended by user cstross, was (and is) almost criminally cheap and comes with an extra pouch for a -- small -- cellphone (very small: my P910 won't fit).
It's a loose fit, but snug enough, and at the time I had all kinds of ideas to make it into a semi-permanent case, but in the end all I did was remove the velcro and replace it with a magnetic clip (friendly warning: If you plan to do this, remember to either always put your N800 in with the screen away from the clip, or add padding on the front inside). At the moment I'm using the small pouch to keep my headphones in.
In fact, it is so cheap that I have it marked on my shopping list for Expansys: Next time I order something, I'll buy a spare -- or two: I've still not given up completely on my DIY ideas for that case.