I would strongly advice you to use Interface Builder on OS X. Doing it by hand is fine if you want to learn, but you're going to save yourself a lot of headaches by using it on actual projects. It really is quite powerful.
As for Java and C++, it depends on what you're doing and on what platforms. For simple applications you can get away with never seeing the UI code. However, for complicated applications and rich clients, you typically have to do some of the code by hand.
