Do you have Google AdSense on your blog? If you do, it would be well worth your while to check your ads every day to see just what is being advertised. AdSense puts on ads automatically (when you sign up for it) and it's geared toward your blog entries, using key words from your posts.
I checked my blog yesterday and again this morning and have already blocked two advertisers. To block unwanted advertisers, you need to go to the advertiser's website (NOT clicking the ad on your blog because that's a violation of your agreement). Get the exact URL of the site and then take that to Google AdSense. Click on your account and manage ads. From there you can type in the URL. It takes a couple of hours for the changes to take effect.
I'm sort of disappointed because these ads I've blocked are BAD. If I have to do this every day, I'll just cancel my account with AdSense, because I refuse to advertise something on my blog that I don't believe in.