We just got back yesterday from our cruise on the Pearl.
I found that there were always empty deck chairs/lounges available if you went to the upper decks on 13 (look on the aft deck too). Around the pool on sea days, it was hard to find anything after 9 am. Even though it is not "allowed", people still save chairs by putting their towels on the chairs in the morning.
The swimming pools were full during the day while at sea however one of the pools is designated as an "Adults Only" pool so it is easier to find room to swim. If you are a lap swimmer, like me, don't expect to be able to do that activity unless you arrive early in the morning or late in the evening (after 4-5PM). I usually swam laps between 7-8 am and there was no one in the pools at that time. Yes, the pools are heated.
The climbing wall was crowded at times however, if you wait a while most people would only climb once or twice and then leave. On the days when we were in port, there were very few people on the wall. Hours were normally 9-6 on seas days/noon-6pm on port days. If you get there closer to 5pm there are fewer people. I climbed almost every day and waited for 4-5 people to go ahead of me at that most. Once you climb, you have to re-enter the line at the end to do second climb in the same session. Make sure that you take socks with you as you will not be able to climb without them. If you use rosin on your hands when climbing, make sure that you ask for the bag since they didn't put it out for the first few days of our cruise. They will let you climb as much as you can handle.