I don't have ultraplush carpets but my in laws have an incredibly worn and matted carpet that would probably be a challenge for any vacuum.
Its possible there are brush roll wear issues since these are always used machines. Our carpets are the cheapest home depot carpets you can get (we live in an apartment complex), not very challenging to clean and not particularly worn.
Still, in both environments litter in carpets is always a huge problem for the Kirby no matter how many passes I give it, and since thats such an important task for vacuuming it makes the Kirby a no-go for me.
I still have a G3 (finally sold my Diamond edition), maybe before it sells ($60 with hose!) I'll try playing with it and see if I can get better results.
