If you have not enabled google adsense on all of your blogs then you are really leaving money on the table. Google can be used for content, searches, rss feeds and more. Google adsense programs make billions of dollars per year. You will want to get some of that advertising money.
Don't think for a moment that it will bring down the quality of your blog. Most likely no one will even mention it to you, it is possible that you may receive some negative email at first, but soon most people will not notice, but you will notice your increase in revenues. If you prefer not to put advertising on your blog that is fine, but if you choose to do it, google adsense is the program for you. It is simple to use and can be adapted to all kinds of blog.