I don't know about you, but I am a bit of a fetishist over my old TI. I got a little shiver looking at the new color screen.
I've tried some and looked at others. Some seem to do what they do incredibly well, but none have the versatility of a TI. I am sure that when one comes to an app store with the capabilities of a TI the age of the scientific calculator is over, surprised this hasn't already happened.
I have never understood the TI thing. for me math is whiteboards and paper and if they don't work... C, mathematica, and matlab and if they don't work ... whiteboards and paper. where does the Calculator fit in? [I can make the bat symbol on one so there is that but what else?]
It's been a while, but I used my TI for derivatives and integrals, and for finding roots in Diff EQ. That and arithmetic. I might carry around a notepad with Mathematica instead these days. Actually, I suppose you just need a browser and Wolfram Alpha. I used Maple a lot at the time. Does anyone still use it?