DEET just plain works, but I have found that the 3M Ultrathon really does work for a long time with similar effectiveness to the old standby, 99% REI Jungle Juice. Ultrathon is "time-release" and I'm impressed with its performance. The thing with DEET is that you really want to keep it off your nylon gear and then there's that mutation thing... so I use a combination of products in the High Sierra:
--Ultrathon in the liquid pumper, for my legs and arms in the morning
--Picarin spray for use on trail w/o concern where it goes
--Pyrethrin-soaked headnet on my pyrethrin-soaked hat, above my pyrethrin-soaked, light-colored hiking shirt (which I wear over a very light inner layer.
--Pyrethrin-soaked tent body and fly
--wash-off at night to minimize transfer of the DEET and other oils to my bag.
Now, the pyrethrin-soaked tent parts have been compared to similar size and color tents nearby and they do have fewer of the vulturous beasts hanging out on them at night than the tents w/o. The headnets...well, the little fellas seemed unaffected, but I think the cheapo, Coughlan's headnets are one of the best purchases for High Sierra happiness, ever. Ha ha!