See (tye)Re: why a nodelet can be kept against author wish?. Basically, if you noticed a typo, you can go back to your node and edit it. If it's been posted to the wrong section, the janitors can clean that up. If your node is just wrong, you can use the <strike>...</strike> tags to mark the information as invalid, but please also write a small update explaining your error so others can still learn from it. Other than that, just leave the node :)