My iPad is not even 6 months old. Ever since I got it, I leave it charging overnight.
After reading the above, leaving the iPad charging overnight isn't dangerous for the battery? I have my iPhone 4s which is around 4 years old and the battery was perfectly fine on iOS 6. No crazy drainage. Soon as I updated to iOS 7, hell broke loose. The battery was unstable and the phone would die within 5 hours.
I have heard that using your phone while it's charging can be dangerous. I guess that's why the iPhone Cables are so short.
I do that a bit sometimes through a wall outlet but I do use the iPad mostly when it's plugged in to my PC via USB but it's technically not charging then. iPads don't charge via USB to PC as far as I know. There is a program which enables the charging but I don't want to mess with the battery too much.