Somehow it doesn't surprise me your guild considers 5/5 normal impressive.
It was only difficult in the sense that it was new and fresh and unknown, and we were undergeared when we did it because we jumped right into raids.
By the time most guild get around to the raids it'll already have become much easier, partly because the mechanics will have been laid out (especially for Soa, who was surprisingly complex to learn compared to the rest of the instance) and partially because people will have been doing heroics for a while and gearing up in preparation, seeing as heroic 4 mans drop the same exact gear as normal 8s.
As for hard/nightmare, as far as we can tell the mechanics are the same, though it's a much larger gearcheck - the first boss alone had about 50% more HP than he did before, did between 25-50% more damage, and had the same enrage timer. Again, only difficult because we're doing it so early - with more gear, it becomes a matter of just knowing the mechanics, which are relatively straightforward.