If it happens in one particular app, you can also try killing that apps' process. It is harmless, doesn't delete the app or any saved data.
To "kill the app", do this:
While the offending app is running, hold down the Sleep button until you get the "Slide to power off" screen.
Instead of sliding, just press and hold the Home button until that screen gets canceled and you get put back at the Home screen.
Your app that was acting weird should be back to normal. I use this most when my Safari freezes. I've also used this on apps that were "working yesterday, but keep crashing today".
This fixes the apps. I've only had to do a hard reset maybe three times when the whole iPad froze up and I couldn't even get the Home button to respond.