I use synthetics almost exclusively on all dry fly wings now. About the only hairwing flies I tie in quantities of more than a dozen or so a year (and we're talking commercial tying here) are blond CDC & Elk caddis. I generally use Widow's Web on everything else, from stoneflies to mayflies to caddis (Clacka Caddis and V-wing caddis cripples).
Owner, Yellowstone Country Fly Fishing
Head Guide, Parks' Fly Shop
Fly Designer, Montana Fly Company
Author, Yellowstone Country Flies and River Characters