Happily, all I needed to do to get a building permit is pass Rescheck, which I barely managed under IECC 2006. I believe that tradeoffs within the envelope are still possible in IECC 2009 (more insulation here; less there) but no longer between the envelope and the mechanical systems. I also believe that you can hire an energy designer to make your passive solar case as an alternative to energy codes, but you'd want to check that out where you live. Regardless, passive solar/high mass got tougher to do, and that's terrible policy in my book.

Obviously, the windows that aren't heat contributors in my house -- three small ones to the north for cross ventilation -- are low-e.

I am relying on Heed to answer the rest of your questions. The software says my home will stay between 55 and 85 with no HVAC. Two owners of passive solar houses in my area say they do much better than that. One says he fires up a masonry heater once or twice a month. The other says he stopped using his propane furnace when the kids left home, and the coldest the house has been on its own is 62. Bear in mind that so. central pa at 5000 HDD straddles the line between north and south, literally and climatically.

Heed's hour-by-hour analysis suggests that there would be very few daylight hours in winter when my windows won't contribute btus. While it is true that low e would retain heat during daylight hours, low emittance would be a statistical blip on the days that count. The brightest day on record here would have poured an average 50k btu/hr through my windows into a house with a design loss of 25k btu. Even on a normal sunny day, I would expect to see 25k btu/hr at some point. What's critical is buffering the heat during the day and holding it at night.

This isn't for everyone. My skill will be measured in temperature fluctations. Consider also intense light, UV damage, cold spots, long warmups after winter trips and more. In fact, I see window treatments more as a livability issue than an energy issue. Firewood is free around here, but closing blinds is much less work.