This topic is mainly for brandables. EMDs, generics etc....don't need logos.
In my opinion logos have the ability to do many things. A bad logo makes a great domain look bad and a great logo makes a bad domain look great.
I believe that the logo is far more important than we can ever imagine. Those that buy brandables in the tech field understand good design and are very visual. Car design, home design, watch design etc......they avidly follow these categories and know the difference between good and bad design. Logos are no different and that first impression could be what makes or breaks the sale. I believe it's better to have no logo then a bad logo just for this reason.
I've said it before and I'll say it again, impression is everything and if you do use a logo make sure it doesn't take anything away from the name.
A bad logo cheapens whatever you're selling.