I have a task killer. I think it has helped my new incredible. It has been a benefit to when I am trying out apps. What do you think? Is it causing instability? Affecting the OS? I am not sure. Explain what you think.
In regards to task managers, Android Central has published an article about it, I've posted some info in the FAQ, and there's also a lot of existing threads about it as well if you'd like to add to them.