I've found that many people who are reading my book are new to programming and are iPhone application developer wannabes. Having the forum has provided a place for these "newbies" to come and join in discussions and ask questions without feeling intimidated or getting flamed. On the contrary, other forum members have been extremely generous with their time, and the forum has become a valuable part of the learning process for its members—and for me as well.
If you have Programming in Objective-C (either edition), come to the forum. I look forward to meeting you there!