Well, I've had it for a few weeks now and have only made £1.95 (I don't know how much that is in dollars, probably about $3 though), but as I say, I spammed it at first so I had no results for about a week. I also don't search things a lot as I tend to spend most of my time online on social networks and forums, so I'm not exactly a fair representation of the average Qmee user.
But I've heard of people making about $8 a week. If you need any hints, try searching things like cheap insurance, gadgets and games console bundles - but don't do it excessively or they'll realise you're spamming! Also, alternate between search engines as much as possible.