I have a passive/active solar house. It works great. I live in Maine the temp is about 15 right now [Linked Image] so as you can imagine heating is a concern. I installed the SOlar hot water system, not sure what percentage of hot water it generates but the other day it was 5 degress out and the collector temp was 150 degrees. Its been working flawlessly for 15 years with 1 maintenance issue. The differential controller failed within a few months of startup. Since then absolutely nothing has broken.
As far as the passive part of my house goes, its nice but I wouldn't do it again. I'd still orient the house toward the south but I'd limit the windows and spend my money on insulation.