I'm a skeptic, and I was slow to embrace mosquito traps. They sounded like a good idea, but there wasn't a lot of information on results, and they were a bit pricey.
Well, we finally got tired of being chased out of the pool at night by the little blood suckers, and decided to take the plunge. We looked at them all, and ended up getting the Skeeter Vac by Blue Rhino.
To my surprise, the thing actually works! Click on the picture above for a close up of a recent night's catch. When we first started using it, the haul was much bigger, but after a couple of seasons of operation we've effectively reduced the mosquito population in our backyard.
The reasons we chose the Skeeter Vac over the Mosquito Magnet were price and ease of operation. The Skeeter Vac models run entirely off of propane, there's no power cord required. Being able to locate these things where you need them is crucial to their success, so this is a huge factor. Plus you can get a top of the line Skeeter Vac for the same price as a mid level Mosquito Magnet.
Now this isn't an overnight cure, but after a few cycles, you'll really notice a difference. Placement is key, so spend the money and get a wheeled one if you can. It will make life a lot easier.
The unit needs to run 24-7 to be the most effective. A 20 lb tank of gas will last two weeks, and I usually change the bait and the tack paper every other tank swap.
I've noticed at the start of each season that it doesn't seem to perform at it's full pest killing potential until it's been running for a few days. I guess it has to warm up to the job. If you're still not catching much after the break in period, try relocating the unit. You want it near the source areas, and away from you.
Northline has a 30 day free trial program on some models. They carry both brands mentioned, as well as a few others, and have a nice comparison chart.