For a few years I've had AdSense at Kartones.net. It is a fast and usually reliable solution to earn some money to pay the hosting fees.
I've had other systems with different degrees of success and requisites (in some I could format the data, in some I was able to clearly state "this is an advertisement"), but it is very common to see AdSense everywhere, because even if nobody clicks on it, you earn one cent per thousand impressions, so with a decent traffic you always will earn something.
I both had normal AdSense banners (mostly text-only except in one or two blogs) and for a while, inside RSS feeds (by using FeedBurner AdSense feed integration).
The irony is that I've always defended the use of AdBlock and similar anti-ads tools/extensions. I have a big hosts file with some hundreds of IPs blocked, I use AdBlock & FlashBlock both on Chrome & Firefox and in general I am the kind of guy that if is going to come back to a website, will spend time "cleaning" it of ads (or abusive plugins that slowdown my browser). I not only have opted out from Google Analytics, but directly blocked the host too .
In fact I'm in the process of building my own micro-analytics suite to remove it from my websites too.
The motto of my blog (and in general in life) is "be the change you wanna see in this world" (from Gandhi), so this is what I did to apply it.
After a few months with the RSS ads I decided to fully remove them for being too annoying. Some of my friends were so happy about that but didn't told me before, so I guess more shy readers were also pleased. It wasn't generating any revenue (just hits/impressions).
Then, I did some maths and checked how well were my yearly earnings with AdSense in general. Conclussion: Not bad but neither impressive, so why bothering readers in search of information landing on the blog posts? I have a job, I can pay a good hosting provider without suffering and I won't get rich by having ads in Kartones.net so... I took the decision of removing them too from here.
After removing them, something interesting happened. Instead of having a general channel for all AdSense banners (like I was doing before, I configured a few ones for the other websites where I have left AdSense on. After a few weeks... the income was still similar by using only those channels. With way less impressions, I was getting similar earnings.
And at the same time, by placing the ads on other places where they might be of interest (as they are context-aware, they tend to show accurate targeting ones) I keep some small earnings each month.
Ending note: I also had other Ad systems apart from Google. I ended up removing them too from Kartones.net. Only the donation texts and/or buttons here and there have been kept (and trying to not distract from the real information).
Update from mid-2012: I have re-added AdSense and donations instead from most places. Donations just don't work and while AdSense doesn't covers even the monthly hosting bill, it helps with paying a small part of it. I haven't added it everywhere (for example this blog won't have AdSense for the time being).