I was helping someone fix their (yes I'm using "their" here) computer running windows xp (I installed MSE on it, it had AVG installed). Today I found a relevant post regarding MSE (Microsoft Security Essentials) that I thought was pretty funny. Note that when the person ran MSE it immediately found a virus on the computer, where AVG was installed the whole time and did nothing about it.
Here's the included screenshot regarding the post that I saw. Some background information, it was from an article in Ars Technica about Trend Micro calling "foul play" on Microsoft for MSE, citing antitrust issues. If you're interested you can find the article here.
Edit: Sorry for the relatively small picture size, haven't found a way to enlarge the picture from the initial upload.