Frugal and Energy Efficient Living

I used to live on the CA coast where we could leave windows open all the time except for a few days a year. Now we're in southern WA where it gets a lot colder in the winter (high of 39F is forecast today), but not nearly as cold as most of Canada or the interior US. During the winter now, we close the windows at night and try to remember to turn off the heat and open the windows for a couple of hours a day. It gets pretty stuffy if we don't - even moreso when one of us cooks.

I remember reading years ago that there was possibly an increase in asthma or other respiratory ailments when buildings (especially office buildings) started getting more energy efficient in the 70's and 80's - basically they were being sealed up to avoid heat or cooling losses.

Is ventilation being overlooked? Is there already a solution I don't know about? Am I just a spoiled ex-Californian?