Today I noticed for the first time that you can't add more than 20 apps to a single folder. The app in question would not go into a folder with 20 other apps but would go into any other folder with less than 20 apps.
I read a thread this week where they could not add an app to a folder but nobody had the answer he needed. I tried to locate the thread unsuccessfully. I wonder how many iPad owner are aware of this.