When I was in high school, Zshell (an exploit that allowed running native Z80 assembly on a TI-85) was all the rage. The exploit and various apps (mostly games) spread virally throughout the school. I did some Z80 assembly programming myself, and it was a learning experience arguably more useful to my career than anything I learned in high school...
Years later at college, when my old 85 had been handed down to a younger sibling, I found I needed a graphing calculator for a physics class. I bought a TI-89 and was impressed to see TI allowed it to run native software, no hacks required. (There were still hacks, to get around a few limitations such as code size, but even these limitations were relaxed in later firmware versions.) I spent far more time programming the calculator than actually using it as a calculator.
Now they're back in their lock-it-down mode? Shame. It always disappoints me when manufacturers go out of their way to make their devices less useful--and in this case, a less capable learning tool, for budding programmers anyway.