I come across a few problems when I switched from 2004 to 2005.
AutoDork changed the plot dialog box and the entire enterface, so plot styles over a network were extremely slow. 2005 sp 1 fixed this.
AutoDork also changed a few of the commands, so some of my lisps and scripts didn't work anymore. I just asked a few friends from the Lisp forums to help out and they now work like a charm.
I think I've come across a few other little things like these, but spent a little time and they work now.
All the new features are great.