I bought the TI-89 I currently use a little over a decade ago and the TI-89 wasn't new then.  Needless to say, the technology used in this calculator is a bit dated, but the utility is undeniable.  Even today, with tools like MatLab available, I find myself relying on it to solve systems of equations and simple integrals and differentials.  The scripting language used to write programs on this calculator is relatively easy to learn, that also gives you a huge amount of functionality.  The unit handling in this calculator allows you to put the units inline with your calculations and the calculator solves with them, allowing you to convert units and to do automatic unit analysis.  This allows you to avoid a lot of simple but common mistakes.  The calculator functionality doesn't end there, I know a lot of people who have used the calculator often and still don't know many of the most powerful tools the calculator provides.