I wouldn't call my MD a backup, more of a car copy. I have an MD recorder (that's right, RECORDER!) in my car dash, so when I get out of the show, I can pop in my MD and enjoy the show on the way home. Gives me an idea how the overall tape turned out. I just run the optical out of my UA-5 to my MD, and the coax. to the M1 DAT. I have to switch discs, but that's not as much of a problem, it doesn't need to be perfect, as it's not a true backup. And if the deck has MDLP - don't bother. It's fine for MP3s, but don't tape a show with it. ATRAC is bad enough as it is.
Oh, and if you're going MD, definately go with a Sharp model. Levels can be adjusted on the fly, buttons are much easier to work in the dark, and menus are very simple to operate. I have a Sharp MD-SR60 for taping, a Sony MZ-N505 for MP3>MD, and a Sony CDX-800REC for in the car.