OK, here's my take:
GS had provided us with a functionality which was time-tested and proven. It worked well.
At some point they introduced the Guide Lines principle, which also is useful and is getting to time-tested status as we speak. BUT...
Guide Lines should _not_ replace the Custom Angle. The Custom Angle was a valuable acceleration and productivity tool: it enabled us to do things that Guide Lines are not much good for (I don't think you or anyone else will disagree that Guide Lines are not best suited when you only have a preset direction vector to which you want to enter repetitively parallel or perpendicular elements; Guide Lines take time to form, and you need time to find the reference object, and all this is a time overhead for _every_ element for which you need them).
So, bottom line, for me, is: If the Graphisoft programmers stepped into a code quicksand patch, whereby they entered an area which was too complex for resolution prior to v12 release, that's fine (although not pleasant).
But let them establish this as a hickup; they must work towards resolving it; not just state that they are now replacing the Mouse Constraint method with the Guide Lines.
Our hard-earned money and product loyalty deserves much better than this.
Alex Zachopoulos
MacBook Pro 17" 2.4GHz, MacOS X 10.5.6, ArchiCAD 11 & 12, WinXP, Vista (well, not really Vista...)