I too use a lightweight tent (Big Agnes SL1 - under 3 lbs) because of mosquitoes. I've been in places where you would go absolutely batty in 30 minutes after the sun sets. Some people resort to a bivy bag with a hood and netting. The ultra-lighters (sub 15 lb packs) generally eschew even a lightweight tent in favour of a tarp and so they save the final few oz. That said, I do carry a lightweight tarp (6'x8' 9 oz. silnylon) for day trips or to provide extra coverage (over the camp kitchen). I have yet to be in a place where bugs are not a problem (even the relatively mosquito free Rockies).

But in my humble opinion, if you don't have a peaceful restful night of sleep with bug protection and a decent thickness pad under your sleeping bag, then you are just giving up a lot of NECESSARY comfort. As Mors Korchanski taught us - if you get a good nights sleep, you are better able to cope in a survival situation. Comfort during sleep is not a luxury, it is a really good survival coping strategy.

Although I've never tried one, a version of the Hennesy Hammock looks like interesting solution.