I'll try to answer your question...it really depends on the ship. One the larger Voyager and Freedom class ships the gyms are pretty large and I've never seen anyone wait for on elliptical or treadmill as there seems to be plenty. On the smaller ships where the gyms are a little smaller then you may have to wait for a little while. All of the ships I have been on have had outstanding facilities. They also have numerous activities planned , some cost and some don't. You will just have to check it out when you get onboard.
There is a small fee to eat at Johnny Rockets but it includes all you can eat. You will have to pay for some specialty items though.
Celebrity Eclipse March 5, 2011
Serenade of the Seas Oct 23, 2011