The tiles are going down, progress at last. We are using the Raimondi tile system. It is guranteed to help level your tile installation (within reason). This is the bomb people. The substrate had some imperfections, and this has corrected them, so that the tiles are all the same level, and we're left with a 1/16" grout line. I'LL never install tiles any other way.
The downside of the Ditra is that we can only install 20 tiles per each 50 lb. bag of mortar, so it's been time consuming. We estimate it will take 18 days to finish the job. At least we are working towards the bathroom and kitchen. After the fourth Day we can start building cabinets to break the monotony.