I tried honestly to use the HP 50g, and here are a few objections that put me back to my TI-89. The low resolution (blocky/grainy) HP 50g display is a big detraction from its usefulness as a high-end graphing calculator. Low resolution limits length of equations and number of equations you can see clearly on the screen–one of the major reasons for having a high-end calculator is to allow you to enter/check long equations on the screen.
That being said, the HP 50g has a dedicated core of aficionados. HP 50g advocates will present a list of counterpoints–and their arguments have merits.
Given the feature set and the inevitable eventual sunsetting of the 15+ year old TI-89 series, a new user considering what high-end calculator to purchase should look to the TI Nspire CX CAS.
In closing, I will give strong admonition to students–DO NOT rely heavily on calculators in your math courses–this will only cause you much suffering in later courses. Even if your last math class in college will be Calculus I or II, you will never gain the true richness of understanding if you constantly use your calculator for homework.
A better approach is to do the problems manually, and on occasion check with the calculator.