So you probably know what this thing can do if you've read the description or the other reviews. It can do all the standard scientific calculator stuff, it can graph functions and with some extra programs it can graph curves that aren't necessarily functions. It can numerically approximate integrals, derivatives, roots, etc. You can create programs and it has financial applications, but I don't know anything about them. It's also portable, which is a nice benefit.
The cons are a lack of a CAS, so there's no algebraic integration, factoring, integrating, or solving differential equations to name a few. The resolution is low and there is no ability to do 3D graphs. But these cons aren't enough to warrant the low rating. The proliferation of laptops and FREE programs that perform all these functions and more is the reason.
Did you know there's a free graphing calculator with CAS called Geogebra that you can download? It will do almost any calculation the TI-whatever will, it will graph everything with higher resolution, it will numerically and algebraically (if possible) calculate derivatives and integrals, and you can create applets with it. In case it seems like I'm advertising Geogebra (which makes no sense because it's free), check out the new Wolfram Alpha site as well. Another free graphing calculator, among other things, with CAS, including matrix algebra and curve fitting. There are many more similar programs or sites available.
Of course, if portability is your main concern and you don't have a laptop, then a TI-84 is an option, but I can't think of any reason that a professional who needs a calculator would want this over what I just mentioned. In particular, I don't know of any mathematician, engineer, or physicist (I only know a few anyway) who actually uses a TI. If they need quick calculations done, they'll use a scientific calculator or for more advanced needs, something like Mathematica or Maple.
This leaves the students and parents who are told that this calculator is a must-have, that it will be used throughout their entire career as a student. I'm a high school math teacher. These are not necessary. A calculator may be necessary at times, but believe me, a scientific one will do just fine. Unfortunately, some AP tests deliberately put problems that require a numerical answer and can't be done by hand in any reasonable amount of time. If this applies to you, you may have to bite the bullet and get something like this. In the meantime, students and parents should be asking their schools why these outdated machines are used in place of better, cheaper options.
Summary for the lazy: If you would pay full price for a 10 year old TV instead of taking a free lower end 2009 HDTV, then buy this item.
Texas Instruments TI-84 Plus Graphing Calculator
