Can you tell me what he didn't like about it? I'm actually considering renting one, mostly because I am fair skinned and will need a good amount of shade to stay at the beach all day. I'd hate to make my family head back to the ship early just because I needed to get out of the sun for awhile. With 4,000 people on board I'm just paranoid that I won't find loungers with umbrellas on the family beach or if we do that one of us will have to remain at our spot all day so that it doesn't get taken, are my fears crazy??
Hi, well, first let me say there will not be 4,000 people on board. I think I explained that earlier in the TR -- we asked a CM and he explained how the ship is considered "full" if every room was filled with a certain # of people (they have a formula) it would be able to hold 4,000. But there is something to the total # of people per cabin and where those cabins are (which side of the ship) based on the lifeboats, etc... so our cruise, for instance, was 3400. And as I said, I never knew there were other people on the ship unless it was time for dinner, or other key moments!!!
Regarding the cabanas... we have rented cabanas at resorts before (not Disney -- only seen those at the Contemporary?). But the ocean, the pool, in one case, was not sectioned off for those of us who paid to have the covered cabana space, or the covered lounges, etc... He didn't like that they had arranged a "private" beach area and ocean access. Now I am not saying there is anything wrong with it, for anyone who does it, seriously, we thought about it for my inlaws in November. But the price was a bit high, and the idea that some of the beach was "cabana renters only" just didn't sit with him -- he would have felt weird. Now it isn't much different from concierge level on the ship -- I mean they have a separate lounge, etc., and that looks very nice, and you are paying for that exclusivity, so I get that. It was just how he felt about it, KWIM? I did hear of people/families splitting the price for one, so that seems more economical, and I think it would be nice to have a place to hang out that wasn't in the sand! There are lots of umbrellas. I think the benefits would outweigh any sense of akwardness depending on the situation. If we were going in high summer with the inlaws I think we would have done it regardless ... I guess Disney wanted to ensure that people in the cabanas had beach access and didn't have to fight for chairs!

There seemed to be plenty of lounges, but it is a perk not to have to scramble. Some people on the boards were complaining about not getting enough "service" -- I didn't read them too closely. They look nice.
If you bring your towels, flip flops, etc. No one is going to move that and take your chairs... at least I don't think so. Just leave something on them... drink cups, water bottles, book, etc.