I have had an MF back on a Hassie for a few years now, and I also own a Leica M9. Neither has an AA filter, and to me this issue is simple. It is all about the glass. If you have really great glass, you want nothing to prevent all the detail from being captured. Pro technique is of course required but assumed because few hobbyists could drop $50K on a camera or make big monthly lease payments. Someone who can legitimately make a case for owning this stuff has been getting paid for delivering the goods to art directors, etc., general expertise for a while.
Given NIkon's new 800s you can enter this rarefied environment for $3K, plus glass. There are new rules here, and folks all over will be experiencing them as the 800s become more prevalent.
Now understand there are no "affordable" MF or frankly Leica lenses, at least not new. The average prime costs the same as a Nikkor mega lens, like the 200mm f2, $5K+....and the quality is readily evident, no question asked.
So if you are using the serious pro Nikkor glass, AND again assuming proper technique for a hi-res camera trying to achieve top results, then buying anything with an AA filter like the D800 would be a mistake, IMO. Frankly, there are a lot of inexpensive Nikkors whose performance at best is comparatively lousy when you have a hi-res capture device, and this discussion would not matter.
Pro technique involves many things, but knowing the effects of diffusion in any given situation...it is not always the aperture alone. Achieving maximum effective sharpness is different from simple numeric resolution...and this is the real goal of a hires capture device...to get you to that max possible with as many options as possible.
One thing I have not taken into account is people using this camera for everything, or for something for which it is not best-suited for (like low light rapid action)...to me that would be akin to having just one hammer in the toolbox. Maybe that would call for the need for the 800....BUT IMO horses for courses, if you have a hi-res camera use it when its strengths are needed.
Honestly, I can count on one hand the number of times I have seen moire in a capture...it is not like it is a regular occurrence. I choose to shoot with the MF when I have a fairly static subject, and I am doing a billboard, banner, show panel, etc. or the art director demands it.
Truthfully, if the subject is dynamic I would rather have the Nikon in my hands. You would be amazed how many large format images printed on banners or walls are Nikon + Photoshop...with all the tricks available today, it is easy. 20 years ago, I did it all on 8x10'" if I had to go that big.
Personally, I will try the 800E, I have one coming, but most likely I wait for a pro version. I hate the lack of integrated vertical grip, SD cards in general, moreover the inability to have 2 identical mirrored cards as I do in my D3s.
It will however, show just how good the Nikkors are when compared to other hi-res cameras. Should be fun.