iPhone and keyboard usability

The iPhone has numerous features that set it apart from the competition. The great user interface has made people to think that it is the most technologically advanced phone on the market.
However, nothing of this matters if it is not usable from the start. That is why it is important, in these initial days, to verify how usable is the iPhone user interface.
The main element of this interface is clearly the keyboard. Other cell phones have integrated keyboards that can be used very predictively. The iPhone, however, has not fixed keyboard. Who guarantees that users will be able to learn how to use the keyboard?
Some people in the blogsphere have started to dissect this very feature of the iPhone.
For example, this post provides a discussion of how the iPhone keyboard interaction might be. The keyboard system will probably have to very smart to avoid confusion when users type of the screen.
In fact, according to Steve Jobs, the iPhone has a sophisticated system that can predict, or correct, what users are typing in order to avoid frequent mistakes. He has also said, however, that users might take some time to get used to the style of the new on-screen keyboard, with keys that auto correct all the time.
It remains to be seen if this very feature of the iPhone will not be one of its major weaknesses. If that happen, then users will enjoy the visual of the iPhone, but will have to stay open to more traditional options such as the Blackberry and similar systems.