Regarding the map shift issue, I once had a shift of approximately five miles after about as many hours airborne. Upon checking the FMC Nav pages, for whatever reason the FMC had gone into IRS Nav Only, ignoring external inputs. I have only seen this happen on that one occasion, and can't rule out the FO playing about with the FMC while I was in the loo, but it could have been a glitch of some sort; I've seen the FMC inexplicably throw its teddys out of the cot many times when it doesn't like a certain route or profile adjustment. That's why I don't allow the descent to be started without some appropriate raw data backing the FMC up, which doesn't seem to be taught - my current employer is the one operator I have flown for which does not require the SID or STAR to be backed up by raw data, and the cadets seem to do it more to humour me than than in an act of self preservation. If that sense of distrust of the automatics and FMC were more prevalent, then perhaps this crew would have started their approach in the right place. It still doesn't explain the loss of control in the GA, though.