I have a TI-89 Titanium, and I almost never use(d) it.
Outside of class,
WolframAlpha is far better for calculus purposes. Excel 2010 is better for statistics and engineering formulas.
The USB link is nice in principle, but slow and really not all that useful. I've had the same idea about loading notes into the calculator, but implementation details like actually preparing machine-readable text instead of a handwritten formula sheet made it impractical. And those calculators are so backward that they use AAA batteries, and can't be recharged over USB. (That alone makes it an artifact of another decade.)
In test situations (if calculus/statistics/etc. must be done by hand) I use a
Casio FX-991s (the
same one I've been using for around 10 years). It can do statistics in a pinch, but there's not really much need for that in a test situation.