Some hikers do this. I can't. The rain shell is just not breathable enough -- I sweat too much when wearing it, unless the weather is *very* cold and windy.

The wind shirt is the perfect "just right" layer for much of my fall-winter-spring hiking. It goes over my base layer while hiking on cool or windy days, or it's my warm layer when I stop on warmer days. I have two wind shirts -- a Marmot Driclime 2-layer windshirt for winter use, and an LL Bean 3-ounce single-layer version for fall and spring.

These work well with a 4-layer clothing system: base layer, wind shirt, insulation layer, and rain shell layer. Bring the appropriate versions of each layer for the season. (Example: down jacket in winter, very light microfleece zip tee in May.) Mix and match as needed for the weather conditions.