Our boat is in charter with the moorings and we enjoy the program. Whether or not the program makes sense depends a lot on how you use it and plans following the end of the program.
What do you want to know about owners time? If an owners has unused time, they can sell it - depends on the contract, but typically two weeks worth. There are some limitations though. Sailonline.com lists owners time that's available and is also a good resource for charterownership info.