Anyone ever go from full frame to crop?

No, but I think I kind of see what you may be touching on.  There are reasons for both.  But the only drawback in my case would be using my A-900 in crop mode doesn't get me the same megapixels as would an A-77 or another 24mp equivalent APSC camera. Not that I need them.  But the D-800 would be an exception.  It would be the only camera that would give you close to both worlds.  Now I can do the same almost with my A-900 as shooting the A-700(less 2mp).  But when you figure an A-77 gives you this feature in 24mp's it makes you think really hard whether you want to go FF.  I'm in FF for the coverage area(FOV), and I don't want to give it up.  Hope that helped a bit. 

--
Glenn
I'm kinda partial to video, but I'm hangin!