Though I haven't used my headnet in years, I will NEVER, EVER again hike without it, at least when temperatures are above freezing. Not only can mosquitos and other flying insects drive you crazy, but they can cause health problems when they get stuck in your ears, and they can cause you to trip and fall when they attack your eyes.
My net is made as follows: Cut two pieces of netting 27.5" long by 21" wide, sew together on three sides with 5/8" seam, square off top using 5/8" seam to form open-ended sack 22" long by 10" square. Sew small stuff sack with shock-cord closure. 30 grams, including small stuff sack. This very simple net works well for me with a wide-brim hat. Normally, I let the net hang loosely in front rather than tucking it into my shirt. This allows some ventilation while still keeping most of the bugs away. You can cut the weight slightly by using that lightweight no-see-um netting from thru-hiker.com and/or by not having a stuff sack.