I've flown on it a few times now with Singapore, London to Sin.
As others posters have mentioned, it is eerily quiet and takeoff is a little underwhelming.
Sitting on the upper deck can seem a little crammed, with the curvature of the fueslage, but in cattle class, you do get a bit more room at the window seat (extra hand luggage space with Singapore at the side of the seat).
If you like gazing out the window, don't sit anywhere near the wing - it huge and you won't see a thing.
The other thing I have noticed is that the overhead bins are massive.
Overall anytime I head to the southern hemisphere I try to book on an A380 - main reason is I always seem to be a bit more refreshed when I land - possibly something to do with better air quality (or great Singapore service!)
Always interesting to see the number of passengers taking pictures of the beast before they board!
Enjoy the flight!