Apple is not likely to charge for the iOS 5 update, however there has been no official word from the company. Original iPad owners were promised that the update to iOS 4 would be free of charge.
In contrast, earlier iPhone OS updates to the iPod touch had a price of $10. Recent updates from Apple on these devices have been free.
Apple has yet to charge iPhone, iPad or iPad 2 owners for an iOS update. It seems that Apple is moving away from charging for the mobile operating system as most of the profits come from other sources such as hardware sales and the App Store.