Sure, moire can corrupt an image, but it's rare. I've been playing with some RAW images from a 5D that had the AA removed by Marc McCalmont (he generously lent them to me to examine). I see a lot more false color fringing at high contrast borders than moire. The high contrast edge color fringing is eliminated pretty much 100% by the Lightroom, remove color fringing from "all edges" command. . . .
And, yes, the files are sharper. But I'm not sure it's a very significant difference, after I go through my normal sharpening routine. I'm trying to figure out if I think I can make a good enough 30" print from a 5D without AA filter to make it worthwhile. At this point, my tentative conclusion is that whether the 5D has an AA filter or not, the maximum print size that I feel is of exhibition quality does not change -- usually 24" in the long dimension, though for some images I can go to 28" in the long dimension (again with or without the AA filter). What's missing from the 5D prints when you enlarge them past 24", to my eyes, is not sharpness but detail. The detail is in the files with the 5D with AA; it's just not as sharp. But the files are sharp enough, when properly post-processed. For files from either with or without an AA filter, I find it's important to add digital grain before printing above 18". It adds a false impression of detail that's convincing.