I actually really like them. It makes it much easier to keep up with your room key/ticket. Last trip, I actually lost my physical tickets and two days before the trip I was looking everywhere for them and freaking out. But, since I had paired all my tickets to my MB as soon I got them, it didn't matter that I lost the physical ticket. Had that happened a decade ago, I would have been out thousands of dollars.
I have had glitches. In September, I got to my room after check in, and it wouldn't open. A couple of calls to Front Desk and it was working in about 10 minutes. All in all, we've had positive experiences with it.