How much you make on ads is going to be largely determined by your content.
For example, if your blog contains political rants, you're probably dealing with cynical readers who are NOT going to be motivated to click on ads. Plus ad targeting may be weird. Likewise, fictional stories won't perform well and -- depending on the content -- can accidently violate Google's TOS.
However, if your blog is about word travel, and many of your readers are finding the blog via google searches because they're planning a trip, and adsense is neatly matching your blog with travel agency ads, and ads for package tours, and ads from hotels and tourist destinations and airlines and etc. ... people are going to click to check out the deals.
There are some exceptions, of course. Movie reviews do NOT tend to not make that much money, because the ads tend to be of the scammy, "Free DVD if you complete our survey!" nature. (Translate that to, "We won't send you the DVD. And we're either going to install spyware on your computer or try to get you to give us your credit card number and SSN and all sorts of other bad info.)
You can ban them, but there's always another one ...
(As an aside -- one of the worst offenders for badly targeted ads is E-bay. They're banned from my site for this, and from the sites of a lot of other publishers. But they target pretty much every keyword around with very annoying ads that say "New and Used (keyword)." My favorite instance of E-bay ad spam, before I banned them, was "New and Used Buffy!" in response to a post about Sarah Michelle Gellar. The result, in this blog, was ribald commentary from a couple of readers. Now, Google's mediabot periodically checks pages for offensive content and the readers had used what are called "stop words" ... and Google's response to the stop words was to start serving Public Service Announcements rather than ads to the page. E-bay got banned from my site and the discussion got deleted, but last I checked, I still wasn't getting ads on that page.)
Leva