Jugg - I've seen the same thing as Jim mentioned. You may wind up with a small skeeter-free zone surrounded by a zone with a now denser concentration of them due to the spill-over of the attractant effects.
Cleo - We still swear by DEET down here.
Mosquitto Control in the Keys has officers who actively seek out places where water can accumulate. If you have a rainwater barrel or a pond, they'll give you tiny fish to add which eat the skeeter eggs.
Tickler - Where I grew up, bats really did do a lot to keep the bugs away. Your suggestion right after Cleo mentioned the Keys made me laugh though. Evidently bats don't like it down here for some reason, as you can here...
http://www.florida-keys-pages.com/interest.htm
Jugg - If they're getting thick around you, I'd guess that there's some water being held somewhere that you're not seeing. Maybe in a neighbor's yard, just over your property line. Or maybe just someplace you haven't looked. It doesn't have to be stagnant, just not (fast) moving. Down here they'll put their eggs anyplace that'll hold water after the rains.
Couple of links for you.
Stuff that experts say doesn't work
http://www.rci.rutgers.edu/~insects/proprom.htm
New Jersey Mosquito home page
http://www-rci.rutgers.edu/~insects/njmos.htm