I was disappointed to read today that Hyatt and MGM have decided to end their partnership - this was a nice option for stays in Las Vegas (especially with reciprocal benefits and earning for Hyatt).
You can read more here.
Generally I stay at Caesar's properties in Vegas since they typically have deals that align with my conferences or planned activities. The occasions where I've stayed with MGM I've used the Hyatt links with success. It's unfortunate to see this option end!