CaS - never use my microwave for them - they are too good not to cook in the oven! I put a metal skewer through the length of the larger potatoes to help conduct the heat. Just love the skins all crispy and fluffy inside.
The thing is, being a single bloke who acts on the spur of the moment, 7 mins in the Micro sounds better than 90 mins in the oven. Unfortunately, a few secs either way makes them equally hard, either undercooked or overcooked. WLTM someone with GSOH who knows how to bake taties properly in the Micro. Age and looks unimportant.