It looks like about a third of their slots are down. Something to do with ticket validation, I hear. They've been hand-paying everyone who tries to cash out...including me.
I remember a couple of years back there was a complete meltdown of the MGM system with the whole reservations system etc down for a couple of days. I am not sure if that including the slots, but everything was haywire and people were tweeting photos of massive check in lines because they had to be all done manually. Here are some details on that incident: http://www.vegastripping.com/news/blog/4648/fail-the-mgm-resorts-computer-system-disaster-continues/ I have been in casinos a few times when these glitches occurred, including Aria and The Venetian. They usually last for a couple of hours at most but it is very annoying when you are in the middle of playing and the system goes down.
Happened to me once at Palazzo. Their entire TITO system went down for about 2 hours on a Tuesday afternoon a year or so ago. I felt bad for the slot attendants with people screaming bloody murder because they had to wait to cash out their $8 ticket. Luckily I had just come from lunch so I had my kindle with me and just read, hit the play button every once and a while, and continued drinking. The thing that sucked is if you hit cash out during that time, the hand pay screen would come up on the monitor and you were stuck. You couldn't change your mind and keep playing until they came and paid you and reset it.