My wife and I are frequent cruisers. We have made some 90+ cruises since the 1970s. We have been more than 1200 days onboard many ships. The last years we made altogether 10 cruises on the Millennium Class ships of Celebrity cruise line. The last one started on April 7th 2006 on Constellation it was our first cruise on Constellation and we completed our Millennium Class experience. The 4 vessels (Millennium, Infinity, Summit and Constellation) are mostly alike. They differ only in the interior decoration (carpet colors, pieces of art shown and the more individual decoration of the specialty restaurants). The atmosphere and the ambiance and even the service provided is almost alike. If I should rate the Millennium Class ships my first would be the Constellation, second the Millennium, third the Summit (but they are very close to each other) and within a small distance on fourth place the Infinity.
We never had other than balcony cabins. On the last cruise (or to be correct there were three cruises in a row) we started in 7198 and changed after some 12 days to 9058, both in the Concierge Class category. All the cabins we ever had were very well equipped and mainly in excellent condition (maybe a small spot somewhere on the floor, the chairs or the sofa from preceding passengers). Space is sufficient everywhere, in the room itself, the bathroom, the balcony and the space for storage in the wardrobe and the drawers even for a four week cruise is ample.
Changing of cabins is smooth and easy. You just have to pack what is in the drawers. Everything hanging will be taken like it is and will be hanged in the same order into the wardrobe of the new cabin. The changing of cabins does not take more than about half an hour.