I found this fascinating Post today:
Have you ever wondered about all of those plugins that you use every day to extend and monetize your WordPress blog? As we all know plugins are very popular with bloggers especially WordPress users. I know that every day when i login to my WordPress blog the first thing i do is check the dashboard for any highlighted issues that need attention. If you have a lot of plugins then you are more than likely going to have to upgrade on more than one occasion. Here then lies an opportunity for you to earn some residual cash from someone who is more than a little familiar with WordPress plugins.Max, Plug Your Blog for Cash, Sep 2008
You should read the whole article.