Once you get used to it, it's really hard to go back to "regular" calculators....
I bought an HP41CX in college for $300 after trying to crunch one lab's worth of wind tunnel data with a "regular" calculator. Saved my ass, it did.
I loved that calculator.
My senior year at UT I had an Energy Systems class that had us analyzing several different components/systems used in power plants. One of the things we did was run tests on a configurable heat exchanger we could run as a 1-2, 2-4, 4-6 counterflow and parallel flow heat exchanger. The lab has just bought a new BASIC computer/Data Acquisition System to take and reduce the data from each run. About halfway through the class that day, the computer crapped out and it could not be re-booted. The professor was about to cancel for the day, when I volunteered to use my TI-59 and printer to do it instead. It took me about 20 minutes to write and debug the program, and then the other guys in the class would call out the data to me and I would enter it. It took a lot longer than the computer/DAS would have, but it did save us from having to come in on a Saturday to finish the test.