Perhaps the ultimate compliment is that after agonizing over which one of these super handhelds to buy I was pleased to discover that with the TI-89 I made a very good choice.  I have already become fairly proficient with it and I'm a non-mathematical person.  The supplied manual walks you through each environment with examples that orient you quickly.  I was able to use it for what I wanted it for suprisingly quickly.  Before long you begin setting it up and using it with little if any reference to the help.