I always think that you are simply attracting more mosquito's to your area. Just like Bug Lights. The ones that wouldn't have been there are attracted to it, and now are in the area. I understand it traps and kills them. Just seems counter-intuative. But, sounds like scott_b has had a good experience with them. I've not had one, but my wife tried the whole yeast/sugar mix in a 2 liter bottle type trap, and that didn't work at all. Supposed to give off the CO and catch them kind of like the hornet trap with sugar, but they never went in there.
I use a lawn spray from Cutter called BackYard Guard. It works really well. Kills and repels them, lasts 4 to 8 weeks. You just spray it out of the hose. There is an Off version as well. This year for us in MN, we've had such a wet spring, it's been difficult to manage them, but just thought I'd give you another choice. Good luck!!!!!