RPN seems to be dying off, but I use my HP48GX almost every day, and it's almost 10 years old. I like RPN for most calculations, once you get used to thinking in "stack" mode it gets really efficient. I use Mathcad for crunching long algebra. I would like an HP emulator for my Palm but I haven't found a stable freebie one yet.
I'm an analog electronics designer doing instrumentation, so I do a lot of quick back of the envelope type calculations. When I start needing to keep track of things like tolerances and temperature coefficients I turn to Excel or Matlab.
