I have two blogs both hosted on Blogger.com
One does roughly 440 UV daily and the other around 40 UV daily.
The main one does on average $405.20 per month.
The secondary one does about $10 per month.
Traffic, as stated earilier, is key. However not the amount of traffic but the quaility. This is true to any site though. Keep the traffic highly targeted and keep your blog niched.