They call DEET a repellent but mostly it screws with the beasties sensors. Many times I have been out on a hot summer night near a swamp and watched the mosquitoes bump along an arm or leg. But they don't land or bite. I was told it screws up their ability to detect CO2 and your scent. They can still tell your warm but can't tell if your food.
A head net is a good idea. The place where DEET is the most uncomfortable is the face; around the mouth, makes everything taste like repellent; and around the eyes, where sweat carries it into the peepers. It isn't so bad on hands, neck and around the boot tops.
One thing about DEET. The higher the concentration the longer it lasts. 100% is good for at least eight hours and has some effect for twelve:
http://www.adventuremedicalkits.com/item_detail.asp?ID=0165-7030&series=10900The 30% stuff is only good for two to four hours.
Also, if weight and bulk aren't too much of a problem, like when operating out of a vehicle or camp, consider any of the canned foggers. Working near a swamp if I stand in the middle of the work site and make a slow turn fogging it is quite remarkable how it cuts down on the numbers of critters in a 15' radius. The effect wears off after 12 hours but there is still a noticeable reduction in mosquitoes and gnat populations for 36 to 48 hours. I can get two or three such applications from the average can.
One of the regular problems around here are storms and hurricanes. In both cases the bugs come out full force. If you have been forced outdoors fogging the area makes it a whole lot more pleasant.