ECS is the second largest motherboard manufacturer, last time I checked. They don't come with the bios settings necessary to overclock the cpu on nearly all of their boards, so don't expect this if you get one. They are cheaper for this reason. Warranty wise, they are about the same as other board manufacturers. Quality wise, if you install them correctly with a quality power supply, they are probably just as good as many other brands. You can sometimes skimp on the motherboard, but never skimp on the brand of power supply.
I have a ecs a790gxm-a motherboard that i purchased just about a year ago and it has treated me very well,in fact i have had more problems with my windows operating system than i have had with my a790gxm-a motherboard and right now i am running at ddr2 1066mhz ram(8gb) without a prob and also i am running two ati radeon 5850 on it as well so no complaints here.i also have a ultra x4 1050 powersupply running all of this incased in a coolermaster haf 932 case.i would recomend ecs to others.there last bios update for my mobo made it compatiable with the anthlon ii so that saves me a load of money if i ever want to go am3.