I was running LMDE 201109 and decided to update the darn thing last week. Wish I'd left it alone TBH. First problem was that it installed Gnome 3 which buggered up all my desktop settings and layout. Managed to get back to a reasonable looking setup by installing Mate, but had to manually change the layout. Then I had all sorts of freeze up problems, double icons for every app and on at least 4 occasions, I had to do a hard reboot which resulted in my Home directory becoming read-only which could only be resolved by re-mounting the drives.
I've now wiped the hard drive and installed LMDE 201204 with Cinnamon. But this time I've partitioned the drive so the O.S. has only 50Gb to go wrong.
So there ya go....that was my experience of the updater. I'm no Linux expert but I've been using Ubuntu or Mint daily since 2008.