What you may see if you try to book...

The systems at the affected hotels seem to be working sporadically. But as of 6 pm PT, these are screen shots of what I found when I tried to book. Signature seemed to be working OK, for now. Earlier I had not included Mirage, which is the other property on the OPERA system, but just now I tested their site, too, and as you can see they're in the same boat.

Click on the pic to see the images more clearly. I am awaiting reax from MGM Mirage PR. Kinda interesting how each site has different kinds of errors.